Physical and hydrodynamic properties of deep sea mining-generated, abyssal sediment plume in the Clarion Clipperton fracture zone (eastern-central Pacific)

The anthropogenic impact of polymetallic nodule harvesting in the
Clarion-Clipperton Fracture Zone is expected to strongly affect the
benthic ecosystem. To predict the long-term, industrial-scale impact of
nodule mining on the deep-sea environment and to improve the reliability
of the sediment plume model, information about the specific
characteristics of deep-sea particles is needed. Discharge simulations of
mining-related fine-grained (median diameter ≈ 20 μm) sediment plumes at
concentrations of 35–500 mg L–1 (dry weight) showed a propensity
for rapid flocculation within 10 to 135 min, resulting in the formation of
large aggregates up to 1100 μm in diameter. The results indicated that the
discharge of elevated plume concentrations (500 mg L–1) under an increased
shear rate (G ≥ 2.4 s–1) would result in improved efficiency of sediment
flocculation. Furthermore, particle transport model results suggested that
even under typical deep-sea flow conditions (G ≈ 0.1 s–1), rapid
deposition of particles could be expected, which would restrict heavy
sediment blanketing (several centimeters) to a smaller fall-out area near
the source, unless subsequent flow events resuspended the sediments.
Planning for in situ tests of these model projections is underway