An artificial resedimentation was created in the Clarion- Clipperton Fracture Zones, where is one of dense manganese nodule areas in the Pacific, in 1994 for impact assessment on seafloor environment. In order to quantify the resedimentation, an image analysis technique of the seafloor photographs was developed. Subsequent artificial disturbances on seafloor were created in a cobalt-rich nodule distribution field on one of the Mid-Pacific Seamounts in 1997 and 1999. The image analysis technique is modified and applied to these cases. Differences between the original technique and the modified one are presented. Limitations and a possible improvement of the technique are discussed.
During manganese nodule mining in the deep ocean, a large amount of siliceous deep-sea sediments will be recovered with the nodules by a collection mechanism. Most of the recovered sediments will be separated from the nodules and discharged immediately. They make a sediment plume near the seafioor and settle douaa again. In case of cobalt-rich manganese deposit mining on seamounts, calcareous sediments will create the same type plume. Environmental impact research for manganese nodule mining was initiated in 1989 in Japan. The objective is to establish an effective environmental assessment method and to develop some guidelines for prevention of mining disturbance. Following five years of planning and baseline studies of the environment in the Clarion-Clipperton Fracture Zones (CCFZ) in the Pacific, the Japan Deep-sea Impact Experiment (JET) was conducted in 1994 in the Japanese mining claim. Post-experiment evaluation of the area was carried out in order to assess the environmental impacts (Yamazaki and Kajitani, 1999; Shirayama, 1999). A large-scale nodule collection test in a cobalt-rich nodule field on a seamount was conducted in 1997 for the development of Japanese nodule mining system (Yamada and Yamazaki, 1998).
