Clay as indicator of sediment plume movement in deep-sea environment
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Future polymetallic nodules mining in the Central Indian Basin (CIB) will disturb not only the deep-sea sediments but also the benthic environment. Generation of voluminous sediment plume due to mining activity is unavoidable, even if the miner would screen the nodules just above the sea floor. The released sediments on the sea floor would migrate in the direction of the bottom water currents and affect the benthic community. It would be more hazardous when the sediment are discharged at the sea surface, as they would affect the entire water column, including light transmission, photosynthesis and productivity. The sediment plume generated by any mining system would cause long-term effects in the deep-sea environment. In order to predict the potential impact on benthic environment, it is necessary to estimate the quantity of plume to be generated, direction in which the plume would move, and how much distance the plume would travel. For this, the surface sediments in the CIB (5230 m depth) were artificially disturbed and resuspended 5 m above the seabed in 1997 during the Indian Deep-Sea Experiment. Initial studies have shown that the clay content during monitoring-1 phase significantly increased compared to post-disturbance, by 15 and 24% in the disturbed zone (DZ); 3 and 20% at the ends of the DZ; 9 and 18% north of the DZ, and 10 and 17% south of the DZ. Here, it is shown that the clay particles can be successfully used as an indicator of the plume direction as well as to estimate the distance traveled by the plume.
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