First phase monitoring studies of simulated benthic disturbance delineating movement of fine particles in the Central Indian Basin

Abstract

Benthic disturbance due to future deep-sea polymetallic nodule mining would involve extensive sediment plume generation and resedimentation on the sea floor. In order to evaluate the effects of resedimentation on benthic environment, the Indian Deepsea Environment Experiment (INDEX) was conducted in 1997, and pre-, and postdisturbance studies on grain size were carried out. The initial increase in clay content after the experiment, continued to increase further as measured in the first monitoring phase samples, 44 months later. Increase in clay-sized particles during monitoring-1 (M-1) was highest within the simulated (disturbed) zone and to the north of it, which is attributed to the combined effects of disaggregation, abrasion, and powderization of sediments during transportation. Due to this fractionation (breaking up), the particles appear to have remained in suspension over a prolonged period of time after they were discharged in the water column 5m above the seabed during INDEX. The travel effects of INDEX plume appears to be localized and confined within and around the disturbed zone (DZ) as resettlement of fine particles from the benthic plume was traced up to 2 km south and 12 to 18 km north of the DZ. The evidence does not suggest the existence of strong currents and benthic storms in the CIB.