A three-dimensional numerical hydrodynamic model has been developed to assess the environmental impact of benthic cold water and sediments being discharged during the deep-sea mining operation of manganese nodules. The model was applied to the claimed province of Japan in the northeastern equatorial Pacific and resedimentation process of dispersal particulates following after the deep-sea disturbance experiment was simulated. In order to reduce the ambiguity in the computational setting, benthic current measurements obtained through mooring system were assimilated into the hydrodynamic model. Moreover the actual trajectories of the seabed disturber were incorporated into the calculation of resuspended sediment transport. As a result of our study, it was suggested that the settling velocity of particulates was a critical parameter of resedimentation and a value of less than 5 XI0-5 ms- 1 was the preferable choice to account for the sediment trap observations.
Deep-sea mineral resources nowadays are of increasing importance since they may supply with rare metals necessary for the development of high technology materials. In Japan, aiming at the commercial mining of manganese nodules in the future, a series of preliminary research for deep-sea investigation and exploitation have been proceeded for over the last decade. During the full-scale mining operation, nodules lying on the deep ocean bed will be excavated with a towing collector and pumped through a pipe to the surface. While recovering nodules, benthic sediments will be rejected at the collector; however, some entrained sediments will be hydraulically drawn to the mining vessel together with nodules and cold and nutritional bottom water. This in turn leads to a considerable influence upon marine environments because they may cause to a change in flow field, dispersion and settling of the turbidity, inhibition of the light penetration and in consequence perturbation in the aquatic living systems.
