The polymetallic nodule exploration programme (PMN) has already identified one Indian mine site in the Central Indian Basin (CIB) where deep-sea mining activities are likely to start in future: In order to assess the probable impacts of nodule mining on the surrounding environments in CIB, the benthic disturbance experiment was carried out by operating the sediment resuspension equipment (disturber) in the indian Pioneer Area. Results of extensive studies conducted before and after the disturber experiment suggest that noticeable changes occur in the sediment texture, clay mineralogy and grain size parameters. The grain size and mineralogical data has further been utilized in characterizing the sediment plume as well as its direction of movement. We present these results and discuss the post-disturbance effects on benthic environment.
In 1982, India launched extensive exploration surveys for polymetallic nodules (PMN) in the Central Indian Ocean and by the end of 1983, two areas each of 150,000 km2 were identified, of which India was alloted exclusive rights over one of them, from the International Seabed Authority in 1987. The average depth, in the Central Indian Basin (CIB) is 5300m." In future, the nodule mining activity is expected to generate " sediment plume" during lifting of modules from the seafloor. The sediment plume" wilt bring about many geological, biological, physical and chemical changes in the surrounding environment. The turbidity in the water column due to plume will affect not only the life and productivity of the benthic organisms on the sea floor but also the marine ecosystem (Sharma and Rao, 1991). Many authors (Amos et al.,1975; Chan and Anderson, 1981; Hirota, 1981; Ichiyeand Carnes, 1981; Morgan, 1981) have discussed such environmental problems. However, the exact picture of nodule· mining would be quite different than it was visualized earlier.