In the Suo-Nada area of the Seto Inland Sea, Japan, sedimentation rates and the sedimentary record of anthropogenic metal loads were determined by combining the Pb-210 dating technique with heavy metal analysis of the sediments. The sedimentation rates vary from 0.11 to 0.27g cm^-2 yr^-1. Lower sedimentation rates were observed in the eastern part of the basin which is characterized by a bottom with sand and gravel, and fast tidal currents.
Anthropogenic and natural loads of copper and zinc into the sediments are 34 and 326, and 65 and 375 ton yr^-1, respectively. The anthropogenic loads are fairly low compared with those of the other main areas of sediment accumulation in the Seto Inland Sea. The highest level of zinc and copper pollution was observed in the western part of the basin because of waste discharge from an old and big ironworks outside basin since the early 1900's.

View full abstract

Wintertime temperature-salinity properties of the southeastern Hwanghae (Yellow Sea) were analysed, based on long-term hydrographic data gathered between 1961 and 1980. A strong thermohaline front is formed in the area west of Cheju-do (along 33°40'E N in the region bounded by 124°E and 126°20'E) during winter and extends to the bottom. This surface-to-bottom front, running from west to east, divides water properties into two types: one type of low temperature and low salinity to the north of the front and another one of high temperature and high salinity to the south of the front. The existence of the front suggests that there is no northward flow in the study area, a finding which runs counter to the conventional belief that there is the Hwanghae Warm Current carrying waters of high temperature and salinity to the north. T-S diagrams show that in winter the Hwanghae Warm Current Water and the Hwanghae Cold Water are the representative water masses in the study area.

View full abstract

The heat balance of the upper ocean under a land and sea breeze was investigated based on observations of sea water temperature in the upper 300m layer and heat flux across the sea surface at a fixed station in Sagami Bay (35°10'N, 139°25'E) during two periods of two days in August 1980 and three days in August 1981. During both periods, a typical land and sea breeze of 4-6m sec^-1 at maximum prevailed in the observation area. Large diurnal variation of sea surface temperature with a maximum peak around noon LST was observed during both periods (the daily value of the range was 0.9° and 2.5° in 1980, and 1.2°, 1.5° and 1.7° in 1981). It was found that these large temperature variations were caused by diurnal variation of the wind speed which dropped to 0-3m sec^-1 at noon when the strongest insolation (-270 Wm^-2) penetrated the sea and at midnight in association with alternations of the land breeze and the sea breeze. On the other hand, vertical mixing of the sea water caused by the wind stress and/or convection due to cooling at night extended down only to the surface 10m layer. Horizontal heat advection was negligibly small. Therefore the local time change of the heat content in the upper 10m water column was affected mainly by the heat flux across the air-sea interface which was estimated from data on radiation fluxes measured directly on board and latent and sensible heat fluxes calculated by the aerodynamic bulk method. The water temperature below the 10m layer also varied with time and the temperature variation in the thermocline (20-50m depth) was frequently larger than that of the sea surface temperature. However, the variation in the upper 10m layer was little influenced by that below the layer.

View full abstract

Differences in daily mean sea level between Kushimoto and Uragami and daily mean sea levels at Miyake-jima and Hachijô-jima in the Izu Islands are examined during the 1964-1980 period, and characteristics of the typical paths of the Kuroshio corresponding to the dominant sea level states are described.
Sea levels at the islands show three dominant states: high and low sea level states (45% and 31%) in the non-large-meander period (October 1963-7 August 1975) and high sea level state (64%) in the large-meander period (8 August 1975-15 March 1980). This indicates the existence of three typical paths of the Kuroshio, and the states correspond to the nearshore and offshore non-large-meander paths and the typical large-meander path, respectively. The first path is located near the coast thmughout the whole southern area off Japan, the second path leaves the coast around the Izu Ridge and passes south of Hachijô-jima, and the third path is located near the coast over the ridge after meandering far to the south of Ensha-nada.
The positions of the three typical paths are almost the same in the farthest upstream and downstream regions south of Japan between 131°E and 142°E. The nearshore and offshore non-large-meander paths overlap between Kyushu and the Kii Peninsula, being invariably close to the coast, while the typical large-meander path south of Shikoku is located offshore and changes its position meridionally.
At the mid-depth of 400 m the nearshore non-large-meander and typical large-meander paths pass the Izu Ridge through the deep channel between Miyake-jima and Hachijô-jima, while the offshore non-large-meander path passes through the deep region south of Hachijô-jima. The path of the Kuroshio at mid-depth is well constrained by the bottom topography of the Izu Ridge.

View full abstract

This paper describes the characteristics of currents around Hokkaido using a current vector map compiled by chasing the displacement of sea marks on a pair of successive thermal infrared images taken from a satellite, NOAA-6. The points of some sea surface patterns showing distinctive features which can be commonly identified in both images are called “Sea Marks”. This “sea mark chase method” has a great advantage over velocity measurements by boats or buoys, in that it gives a synoptic view of the velocity distribution over a broad sea area extending for some hundreds of miles on a short time scale of half a day.
In order to investigate the current in the late fall of 1981, we used the data taken at 19: 05 JST on 30 October and at 7: 20 JST on 31 October. With these data taken with a 12 hr difference, the measurement accuracy of the speed of sea marks reached ±0.1 knot through geometrical correction. The velocity vectors of sea marks agreed with results of GEK measurements performed on those days, and also with the mean current pattern obtained in the past based on sea surface data.
The most distinct features recognized were some cyclonic and anticyclonic eddies of the order of 100km in diameter which dominated in the Kuril Basin of the Okhotsk Sea. They appeared clearly in the original NOAA images and their physical parameters were determined quantitatively from the vector map. These eddies were located in the region of decay of the Soya Warm Current and were rotating at a speed nearly as large as that of the current. The problems of what feeds energy to these eddies and how long they live remain to be solved in future studies.

View full abstract

Microbial degradation of five crude oils such as Arabian light, Berri, Murban, Khafji i and Minas crude oil by a pure bacterial strain, Pseudomonas sp. isolated from the sea water sampled at Kawasaki Harbor in Tokyo Bay, was studied experimentally in the enriched seawater medium.
The degradation of crude oils was determined in total residual oil and in four fractions of saturated, aromatics, asphaltene and column residue by use of the column chromatography with activated alumina.
The saturated fraction was shown to be most biodegradable. The aromatics followed for all five crude oils examined and the asphaltene was biodegradable to some extent. The column residue was not apparently degraded by Pseudomonas sp. within 30 days. Each of Arabian light, Berri or Murban crude oil was degraded from 59 to 63.5 %, Khafji crude oil 49 % and Minas crude oil, solid at room temperature, only 33%.Degradation rate of the five crude oils was determined to be in a range from 2.88 to 17.3 mg-oil 1^-1 hr^-1 or from 6.0×10^-12 to 1.56×10^-10 mg-oil cell^-1 hr^-1. Relative degradation of n-paraffins of different carbon numbers in the saturated fraction was found to be similar regardless of carbon number for the five crude oils.

View full abstract

In inviscid shallow water models currents generated by spatially uniform winds are transient and are eliminated by Rossby and equatorial Kelvin waves excited at the eastern and western coasts, respectively. The inclusion of mixing processes can lead to an entirely different steady state in which currents are present. It is shown that the mixing of heat affects the steady state more than does the mixing of momentum because the waves that are important in the oceanic adjustment are divergent.

View full abstract

I am extremely grateful and honored for being awarded the Okada Prize (1985) for my study. The present article reviews my research on the distribution, behavior and fate of PCBs in the marine environment. The outline of this study is summarized as follows: 1. Polychlorinated biphenyls (PCBs) were detectable in the wide range of environmental media and biota of the Seto-Inland Sea, Japan, in which much high concentrations were found in sediment and biological samples due to their hydrophobic, lipophilic and less biodegradable properties as well as their extensive production and use in estuarine and coastal regions.
2. PCBs extend the boundaries of their distribution all over the global environment, being evidenced by their occurrence in open ocean atmosphere, hydrosphere and biosphere, even in Antarctica. The global contamination of PCBs is much more prominent in northern hemisphere than in southern hemisphere.
3. The sinking rate of PCBs from surface to deeper layers in open ocean water column is relatively slower in tropical waters than in high latitude ones. This implies the possible prolonged contamination of persistent synthetic organic chemicals in the tropical marine environment.
4. The bioaccumulation processes in marine ecosystems can be explained by the physicochemical and biochemical properties of PCBs and the metabolic capacity of organisms. In higher animals, additional factors such as parturition and lactation are also related to this process.
5. Total PCB load in global environment was estimated to be about 370 thousand tons. Of this, most amounts were in coastal sediment and open ocean water. Presently, about 780 thousand tons of PCBs are still in use mainly in electrical equipments. In order to reduce the PCB levels in marine environment, pertinent measures to prevent the further discharge and safe disposal of PCBs are required.

View full abstract