Numerical Simulation of Deep-Sea Sediment Transport Induced by a Dredge Experiment in the Northeastern Pacific Ocean

Kaveh Purkiani,Jens Greinert,Henko De Stigter,Michael Schulz,Sabine Haalboom,Benjamin Gillard,Martina Hollstein,André Paul,Matthias Haeckel,Matthias Baeye,Annemiek Vink,Laurenz Thomsen

doi:10.3389/fmars.2021.719463

Abstract

Predictability of the dispersion of sediment plumes induced by potential deep-sea mining activities is still very limited due to operational limitations on in-situ observations required for a thorough validation and calibration of numerical models. Here we report on a plume dispersion experiment carried out in the German license area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean in 4,200 m water depth. The dispersion of a sediment plume induced by a small-scale dredge experiment in April 2019 was investigated numerically by employing a sediment transport module coupled to a high-resolution hydrodynamic regional ocean model. Various aspects including sediment characteristics and ocean hydrodynamics were examined to obtain the best statistical agreement between sensor-based observations and model results. Results show that the model is capable of reproducing suspended sediment concentration and redeposition patterns observed during the dredge experiment. Due to a strong southward current during the dredging, the model predicts no sediment deposition and plume dispersion north of the dredging tracks. The sediment redeposition thickness reaches up to 9 mm directly next to the dredging tracks and 0.07 mm in about 320 m away from the dredging center. The model results suggest that seabed topography and variable sediment release heights above the seafloor cause significant changes especially for the low sedimentation pattern in the far-field area. Near-bottom mixing is expected to strongly influence vertical transport of suspended sediment.

Highlights

For economic reasons, deep-sea mining has attracted renewed attention during the last two decades
In order to better understand the dynamics of deep-sea sediment transport, a numerical simulation using a combination of sensor data and seafloor images taken by a Remotely Operated Vehicle (ROV) was carried out in this study to investigate plume dispersal and sediment deposition and underlying key parameters in this region
We performed a small-scale dredge experiment and combined a numerical model with observations from a monitoring array to investigate the spread of the sediment plume and the amount of redeposition induced by dredging

Summary

Introduction

Deep-sea mining has attracted renewed attention during the last two decades. Visual- and sensor data were collected to study the in-situ sediment plume and its redeposition (Haalboom et al, in preparation). To monitor the dispersion of the generated sediment plumes, 15 sensor platforms were distributed at distances of 100–475 m away from the planned dredge tracks. The majority of the sensor platforms were distributed on two parallel lines which were 200 m apart, perpendicular to the WSW-ENE trending dredge tracks. In order to better understand the dynamics of deep-sea sediment transport, a numerical simulation using a combination of sensor data and seafloor images taken by a Remotely Operated Vehicle (ROV) was carried out in this study to investigate plume dispersal and sediment deposition and underlying key parameters in this region

Methods

Results

Discussion

Conclusion