In situ optical measurement of particles in sediment plumes generated by a pre-prototype polymetallic nodule collector

Abstract Results and key insights are presented from in situ, high-resolution optical measurements of particle size distributions (PSD) for sediment plumes generated by a pre-prototype deep seabed nodule collector vehicle operating in the abyssal Pacific Ocean. The data show marked differences compared to previously reported laboratory-based, ex situ measurements. The in situ suspended sediment grain size and other key particle shape characteristics are found to be dependent on multiple factors such as the collector vehicle maneuvers, the time elapsed following discharge, and the complex hydrodynamic processes that generate the sediment in suspension. At the measuring instrument mounting height of 5m above the seabed, the PSD from a highly complex succession of straight-line maneuvers is found to converge to that of the canonical case of a simple straight-line driving maneuver within a timescale of ten minutes. Practically, our findings emphasize the need for parameterization of sediment plume transport models based on well-informed comprehensive PSDs of detrained suspended sediment measured in situ at adequate timescales and in regions no longer actively affected by active and complex hydrodynamic processes.