The radioisotopes 210Pb and 137 Cswere measured in twenty sediment cores obtained from Sagami Bay, Japan. Total 210Pb concentrations of settling particles, collected by time-series sediment traps moored at 350m and 20m above the sea-floor (the water depth of 1550m) near the deep-sea station SB in the central region of the bay, were also determined in order to estimate their settling fluxes. Mean sedimentation rates calculated from the inventories of 210Pbex.(unsupported) in sediment cores ranged from 0.05 to 0.19g cm-2y-1 At SB site where 6 cores were collected, the average rate was 0.11±0.02g cm-2y-1, which was similar to that calculated under the assumption that the age of the 137 peak corresponds to its maximum fallout year of 1963. From the results of t he time series sediment trap experiment, the average 210Pb concentration of settling particles was 264 dpm g-1 in the upper trap and 248 dpm g-1 in the lower one, while the annual mean 210Pb fluxes were calculated to be 388 dpm m-2d-1 at the upper layer and 1392 dpm m-2d-1 at the lower, respectively. The mass balance calculation of 210Pb in the water-sediment column aptly demonstrates that the increase in 210Pb flux at the lower layer results from the lateral transport of particulate 210Pb near the bottom, and suggests that the amount of particulate 210Pb corresponding to ca. 38% of the sinking flux to the bottom is not deposited into sediments but transported seaward through the benthic boundary layer.
Fourteen major and trace elements in marine sediment core samples collected from the coasts along eastern Japan, i. e. Tokyo Bay (II)(the recess), Tokyo Bay (IV)(the mouth), Mutsu Bay and Funka Bay and the Northwest Pacific basin as a comparative subject were determined by the instrumental neutron activation analysis (INAA). The sedimentation rates and sedimentary ages were calculated for the coastal sediment cores by the 210Pb method. The results obtained in this study are summarized as follows: (1) Lanthanoid abundance patterns suggested that the major origin of the sediments was terrigenous material. La*/Lu* and Ce*/La* ratios revealed that the sediments from Tokyo Bay (II) and Mutsu Bay more directly reflected the contribution from river than those of other regions. In addition, the Th/Sc ratio indicated that the coastal sedime n ts mainly originated in the materials from the volcanic island-arcs, Japanese islands, whereas those from the Northwest Pacific mainly from the continent. (2) The correlation between the Ce/U and Th/U ratios with high correlation coefficients of 0.920 to 0.991 indicated that all the sediments from Tokyo Bay (II) and Funka Bay were in reducing conditions while at least the upper sediments from Tokyo Bay (IV) and Mutsu Bay were in oxidizing conditions. (3) It became quite obvious that the sedimentation mechanism and the s edimentation environment at Tokyo Bay (II) was different from those at Tokyo Bay (N), since the sedimentation rate at Tokyo Bay (II) was approximately twice as large as that at Tokyo Bay (N). The sedimentary age of the 5th layer (8-10 cm in depth) from Funka Bay was calculated at approximately 1940-50, which agreed with the time, 1943-45 when Showa-shinzan was formed by the eruption of the Usu volcano.
The present knowledge on the abundance and molecular composition of organic matter and its behavior in recent marine (deep water and coastal) sediments is reviewed. It is generally recognized that the primary phytoplankton production and the length of water column where planktonic debris are sinking to the bottom play an important role in governing the abundance of organic matter in sediments. These two factors also explain the higher amounts of readily hydrolyzable organic fractions, total amino acids and total carbohydrates in coastal sediments than in deep water sediments. A large number of organic compoun ds are now used as indicators of marine or terrestrial biological contribution to sedimentary organic matter. Many kinds of anthropogenic organic compounds, such as oilderived long-chain alkanes, polycyclic aromatic hydrocarbons (PAHs), alkylbenzenes, alkylphenols, bisphenol A, phthalic acid esters, PCBs, DDE, dioxins, coplanar-PCBs, have been measured in the sediment cores from Tokyo Bay. The vertical profiles of those anthropogenic compounds in the sediments are considered to reflect the changes in the input of those compounds to the area surrounding the bay.
Over the last four decades, the Irish Sea has received controlled discharges of radioactive effluents from the Sellafield (Windscale) nuclear fuel reprocessing plant in Cumbria, UK. Enhanced levels of a range of fission, activation and transuranic elements have been detected in a variety of environmental media. Most of Pu and 241Am and about 10% of 137Cs discharged have been retained in a deposit of the fine sediment near the discharge point. The quantities of radionuclides discharged annually from Sellafield decreased by two orders of magnitude from the mid-1970s to 1980, but estimated internal and external exposure for critical group decreased by only less than one order of magnitude over this period. Redistribution of the highly contaminated marine sediment is potentially of major significance. In this paper, a review is presented of published work and our studies relating to the artificial long-lived radionuclides, 99Tc, 137Cs, 237Np, Pu isotopes and 241Am, in sediments around the Irish Sea coast. The dominant mechanism (solution and/or particle transport) of supply of these radionuclides to coastal sediment is mainly discussed.
In order to investigate the chemical form of authigenic phosphate compounds being precipitated in coastal sediemnt, vertical distributions of dissolved phophate and fluoride in pore water from the sediments of Funka Bay Japan, were determined. We found an inverse relationship between interstitial phosphate and fluoride concentrations, suggesting precipitation of an authigenic fluoro-phosphorus compound with a P/F atomic ratio of around 1/3 in the sediemnt. The solubility experiments of biogenic silica were done using the Funak Bay sediments. The solubility coefficients were estimated from temporal change of interstitial silicate in a temperature controlled room of 6, 11 and 22°C. The change of silicate concentrartion is irreversible for temperature, the irreversibility is larger at surface than in a deeper layer. This suggested that biogenic silicate in a deeper layer is more crystallized than at surface.
The mangrove ecosystem and the deposit are developing only upper half of the tidal zone. The ecosystem is stretching like a narrow green belt surrounding the tropical to sub tropical coast. The sediment has the following characteristics: 1. The sediment might be formed up as the results of interaction of not only fluvial and marine process but also the biomass accumulation and bioturbation processes. 2. The organic to peaty material is a distinctive indicator of the sea-level change and the history of mangrove forest. 3. The inner structure of mangrove forest is categorized into three zones. Zone 1 is located near the mean tide level formed by tidal and fluvial process. Zone 2 is formed by man grove organics accumulation and bioturbation which is developing between the mean to mean high water level. Zone 3 is developing between the mean high and the highest high water level that is formed by the process of mudlobster bioturbati on and weak tidal water movement. These three zones develop the remarkable sediment.