An in situ study of abyssal turbidity-current sediment plumes generated by a deep seabed polymetallic nodule mining preprototype collector vehicle

Abstract

An in situ study to investigate the dynamics of sediment plumes near the release from a deep seabed polymetallic nodule mining preprototype collector vehicle was conducted in the Clarion Clipperton Zone in the Pacific Ocean 4500-m deep. The experiments reveal that the excess density of the released sediment-laden water leads to a low-lying, laterally spreading turbidity current. At the time of measurement, 2 to 8% of the sediment mass were detected 2 m or higher above the seabed and were not observed to settle over several hours, with the remaining 92 to 98% below 2 m and some fraction of that locally deposited. Our results suggest that turbidity current dynamics sets the fraction of sediment remaining suspended and the scale of the subsequent ambient sediment plume. The implications of this process, which is characteristically overlooked in previous modeling efforts, are substantial for plume modeling that will lie at the heart of environmental impact statements for regulatory consideration.

Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal

“…Of great interest is the potential effect of BML on the dispersal of resuspended sediment plume from the discharge of deep-seabed mining nodule-collecting vehicles operating at the seabed [14,19,20]. The discharged plume initially behaves as a high Reynolds number turbulent wake (with an outflow Reynolds number Re o ∼ O(10 6…”

“…In the deep water column, a key environmental consideration is the release of sediment plumes generated by nodule collector vehicles traversing on the seabed [19]. The released plume particles would form (i) gravity currents [20] and (ii) associated ambient plumes with suspended small particles (typically with diameter < 63 m) that behave largely as passive tracers [21]. The creation and dispersal of ambient plumes can be considered essentially as the artificial processes of resuspension and transport of sediment particles.…”

Probabilistic ecological risk assessment for deep-sea mining: a Bayesian Network for Chatham Rise, SW Pacific Ocean

“…For the second scenario, hereafter ‘Intermediate disturbance’, 50% of the mined area was disturbed, and sediments were disrupted to less than 10 cm depth. The High disturbance scenario was defined by experts based on the description of a proposed mining operation for phosphorite nodules on the Chatham Rise (Chatham Rock Phosphate 2014), while the Intermediate disturbance scenario was based on the anticipated disturbance from other types of mining operations (e.g., surface nodule extraction as proposed for polymetallic nodule mining, e.g., Muñoz-Royo et al, 2022) and could also be applied to describe low-penetration bottom trawling (Eigaard et al, 2016). All the other variables in the model are further affected by these decision variables.…”

Deep seabed mining: Frontiers in engineering geology and environment

“…In deep seabed mining activities, the collection of minerals, the beneficiation on the ship, and the discharge of underwater tailings have serious impacts on the marine environment, especially plumes (Fig. 23) (Muñoz-Royo et al 2022;Peacock and Ouillon 2022). The mining of 3 × 10 6 t of polymetallic nodules per year is estimated to result in a total volume of 5 × 10 9 m 3 of resuspended sediment (Sharma There can be two stages of plume generation: the seafloor sediment plume discharged during extraction and the midwater plume discharged during beneficiation and the treatment of underwater tailings (Sharma et al 2017;Muñoz-Royo et al 2021).…”