Photographic observations were carried out at depths of the-shelf edge at the mouth of Uchiura Inlet, Suruga Bay, central Japan in order to clarify the life style of the isocrinid stalked crinoid, Metacrinus rotundus (Echinodermata). The distribution of the species was found to be restricted to a nattow atea. where boulders and rock outcrops were locally present. Mean density of the crinoid was 0.05 m^-2, and this value was an order of magnitude smaller than that of the deeper isocrinid, Diplocrinus wyvillethomsoni, reported from the Bay of Biscay. Metacrinus rotundus formed a parabolic filtration fan with its arms recurved into the bottom current, and was thought to. be a passive suspension feeder elevating the fan into the water column by its stalk. The distal half of the stalk lay along the hard substratum and about ten groups of cirri grasped the substratum. This mode of attachment was similar to that of Cenocrinus rather than that of Diplocrinus. Metacrinus rotundus collect food at the layer between 10 and 50 cm aboye the sea floor, and do not utiiize a higher layer even when this layer could be utilized by climbing over a larger boulder. Resuspended benthic materials are thought to be important as a food source for M. rotundus, and the crinoids seek not only locations of stronger currents but also the position where much resuspended matter is available.

View full abstract

Concentrations and inventories of ¹³⁷Cs and ^{239, 240}Pu were determined in sea waters and sediments columns from the western North Pacific from 1980 to 1986.
The ^{239, 240}PU/¹³⁷Csactivity ratio in the water column shows a tendency to increase from the surface (10-3) to bottom waters (10-1), but the ratio in sediment is within a rather narrow range (10^-2 to 10^-1), indicating more effective removal of plutonium from the water column than ¹³⁷Cs. In regions south of 40°N, the radionuclide inventories in the water column significantly exceed the estimated global fallout (stratospheric fallout due to the atmospheric nuclear explosion), especially in the case of ^{239, 240}Pu. These excess inventories imply that local or close-in fallout derived from nuclear explosions in the equatorial North Pacific are well-preserved and retained in the regions, despite about 20 years since the atmospheric nuclear explosion moratorium. Data suggesting lateral transport of ¹³⁷Cs in surface water from north of 40°N to southern regions is shown. Some data on ⁹⁰Sr contents are also shown.

View full abstract

Measurements of subsurface irradiance spectra in the ocean consistently indicate intensities of long-wavelength visible light (λ≥589 nm) greater than could be derived from the penetration of sunliaht. This can be attributed to natural fluorescence and/or to spectral crosstalk due to light leakage through the blocking filters of each discrete detector. A comparison of observed profiles with modelled contributions from these two possible sources indicates that both factors are contributing. At 671 and 694 nm wavelength, the excess signal appears to be predominantly fluorescence while that at 589 nm is mostly crosstalk. Both effects appear to be important at 625 nm although the amount of excess light is small compared to the other wavelengths.
The above observations and interpretations are consistent with the optical design of the instrument used and the shape of natural irradiance spectra. Fluorescence efficiencies derived from the irradiance measurements correlate well with measured in situ fluorescence.

View full abstract

A continuous observation system of ship drift of ferry boats was developed using Loran C, ship direction, ship speed and wind velocity measurement. A formula to estimate the wind-driven lateral drift of the boat is proposed, and a measuring system of the surface current is described, including a discussions on its usefullness to monitor day-to-day variations of the circulation patterns in the coastal boundary regions of the Kuroshio.
This system was applied to observe variations of the circulation in the Kumanonada, and Enshu-nada Seas south of Japan. Some preliminary results were obtained by using this system as well as other methods. This work focuses on the behavior of warm eddies in the Kumano-nada Sea. The surface current patterns that in clude these phenomena obtained by the use of the ship drift show good correspondence with currents and thermal structures observed with GEK, CTD, moored current meters and satellite thermal images.

View full abstract

The difference in the M₂ tidal range, which reaches 12cm between both sides of the narrow (50km) Bungo Channel, Japan is suggested to result from the interference between the incident and reflected Kelvin waves. The spatial distribution of the tidal range in such a narrow channel is quite sensitive to the phase lag of the reflected Kelvin wave which occurs at the head of the channel. It seems that this phase lag is strongly dependent on the volume of the basin connected to the channel.

View full abstract

The behavior of isolated meso-scale eddies near the coastal boundary is studied by numerical experiments based on the quasi-geostrophic equation in a basin on an f-plane. First, Bachelor-modon type eddies are investigated as an idealized model of isolated eddies close to the wall. The first-mode Bachelor-modon type eddy is found to be robust enough to recover its original form even after it turns a corner of the basin. In contrast, the second mode is unstable; it tends to move away from the wall and finally splits into two eddies proceeding in opposite directions along the wall. An initially Gaussian eddy a little distant from the boundary interacts with a Bachelor-modon type eddy translating along the boundary, sometimes resulting in vortex merging and pairing just as in the head-on collision of two modons on a beta-plane. It is found that an initially Gaussian eddy located moderately close to the coast rapidly settles down to a steadily translating eddy, which can be approximated remarkably well by a first-mode Bachelor-modon type eddy not only in appearance but also in translation velocity within an error of about 20%.

View full abstract

I am deeply honored to have been selected as a recipient of the 1987 Okada Prize by the Oceanographical Society of Japan. The present paper reviews my work and recent studies of other investigators concerning mineral aerosol (dust) particles in the marine atmosphere over the Pacific Ocean. I would like to emphasize the importance of atmospheric deposition of continental substances to the ocean environment.
From consecutive measurements of atmospheric dust concentrations and total deposition fluxes at 13 island stations in the Pacific Ocean, a strong seasonal transport pattern of dust particles was found at most of the stations. High atmospheric dust concentrations occurred during the spring in both hemispheres. There was a latitudinal gradient in both the atmospheric dust concentration and flux, with the highest values observed at midlatitudes.
When combined with observations of dust storms in Asia and isentropic trajectory analysis, it was clear that the dust over the central North Pacific was transported by the upper westerly winds from the arid desert regions in central and eastern Asia. Transport times were 1-2 weeks, and in some cases, atmospheric transport paths of over 10, 000 km were observed.
Infrequent short-term dust events contributed most of annual atmospheric dust flux to the open ocean. These sporadic inputs are major sources for both suspended mineral matter in the water column and the non-biogenic component of deep-sea sediments in the Pacific Ocean. The impact of atmospheric dust fluxes on chemical and biological processes in the water column remains to be determined.

View full abstract