Chemical and radiochemical characteristics of sediments obtained from the Japan Deep-Sea Impact Experiment (JET) site. Concentrations of organic carbon, organic nitrogen, calcium carbonate and biogenic silica in top 1crn layer were 0.5%, 0.06%, 0.3% and 13%, respectively. Sediment accumulation rate was estimated to be 0.1 g cm-2 kyr-1 from excess 23ºTh profiles. Organic carbon, calcium carbonate and biogenic silica were supplied from water column to sediment at rates of 100,64 and 70 mmol m-2 yr-1, respectively, however, almost all of the biogenic components were degraded or dissolved at water-sediment interface.


Deep-sea mineral resources characterized by manganese nodules seem to be extremely useful source for rare metals which are necessary for development of high technology industry, and commercial mining of manganese nodules is expected to begin within next 20 - 50 years. However, the mining operation will cause extensive resedimentation over large areas of deep sea floor and it is thought to be harmful to the benthic biological community. It is extremely important to assess the effects of deep-sea mining on oceanic life and environment and to establish necessary regulations and standards for environmental conservation. However, our present knowledge for benthic ecosystem is so limited that we cannot predict the impact of the deep-sea mining. Therefore, it is necessary to accumulate more information on the deep sea environment and benthic communities. To understand relationship between resedimentation and biological reaction, experiments of artificial perturbation of deep sea sediment have been conducted (BIE by NOAA, USA and DISCOL by Hamburg Univ., Germany). The Metal Mining Agency of Japan also commenced environmental studies of deep sea sediment including the artificial perturbation experiment (the Japan Deep Sea Impact Experiment, JET). Biological community is influenced by energy supply from settling particles and characteristic of sediment, significantly.

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