Experimental investigation of near-field plumes generated by deep-sea mining vehicle under different operating modes

Existing assessments of deep-sea mining sediment plumes mainly rely on integrated indicators such as concentration, sedimentation, and diffusion range. This makes it difficult to constrain the formation mechanisms of near-field plumes under different operating conditions. In this study, we used a 1:32 scale mining vehicle and a self-developed Particulate Monitoring and Capture System in a large underwater experimental facility. We observed 22 plume events under three operating conditions: stationary collection (SC), mobile collection (MC), and transit (TR). Second-scale velocity and concentration records were coupled with minute-scale particle size, morphology, and geochemical information. The median interfacial fluxes of SC and MC were 3.34 × and 2.88 × those in TR, respectively, but similar high fluxes arose through different pathways. SC was mainly controlled by enhanced advection, whereas MC more often reflected load enhancement and its coupling with advection. MC also showed stronger near-bed shear, turbulence, and concentration pulses. The mass captured along the near-bed path was 1.81 times that of the upper path, indicating persistent load enrichment near the bed. Particle property analysis further showed that collection operations favored coarser particles, narrower size spectra, and measurable vertical sorting. These results show that similar endpoint responses do not imply a unique transport pathway. Attribute-related monitoring can reduce ambiguity in plume interpretation. It can also provide verifiable constraints for source characterization, near-bed transport, sedimentation prediction, and plume model parameterization.