This research article, “Monitoring benthic plumes, sediment redeposition, and seafloor imprints caused by deep-sea polymetallic nodule mining,” presents a detailed analysis of a deep-sea polymetallic nodule mining trial. The study quantitatively assessed the dispersion of the resulting sediment plume as well as seafloor impact, utilizing various advanced sensors and technologies, including hydroacoustic and optical sensors mounted on stationary and mobile platforms.

Results showed a gravity current forming downslope, transporting the suspended sediment up to 500 meters away from the source. Rapid sediment redeposition occurred, largely within a limited area. Driven by the bottom currents, a small fraction of the sediment stayed in suspension, and the authors note that beyond 1,700 meters, it became increasingly difficult to distinguish the top of the sediment plume from overlying clear water. Sensor data recorded sediment concentrations of up to ~4 milligrams per liter (mg/L) at a distance of 1,800 meters. Measurements taken 48 hours after the trial at 4.5 kilometers from the trial site showed the concentration had further diluted to 0.1 milligrams per liter (mg/l). Visually, at 0.1 mg/l, the water would appear completely clear.

The authors of the study also discuss the implications for future deep-sea mining and improved real-time monitoring capabilities. Studies such as these form the foundation for designing approaches to ecological monitoring, as well as commercial nodule collection that strives to minimize and mitigate the associated environmental impacts and effects to the greatest extent possible.

Background

Since 2018, GSR has been collaborating with the European research project MiningImpact. MiningImpact is made up of 29 institutions from nine European countries, plus the International Seabed Authority, which were partners in the second phase of MiningImpact. MiningImpact will continue into a third phase from July 2025 to June 2029

The MiningImpact project involved scientists independently monitoring GSR’s collector technology trial from a separate vessel chartered and led by the contractor BGR. GSR also collaborated with, among others, the Massachusetts Institute of Technology (MIT), who were aboard the GSR-chartered vessel, specifically to monitor the near-field aspects of the sediment plumes.

MiningImpact Research

Trials of GSR’s Patania II pre-prototype nodule collector took place in the GSR and BGR contract areas of the CCZ in April and May 2021. The studies were and are still being conducted by independent scientists in the MiningImpact project that not only address the direct effects of collecting polymetallic nodules but also those of the sediment plume created by the process.

The data provide information on the ecosystem effects of potential future mining that cannot be drawn from the small-scale benthic impact experiments conducted in the past. By employing state-of-the-art scientific equipment, researchers could determine the spread of the sediment plume and how it resettles. Among the specialized instruments deployed in 2021, there were two remotely operated vehicles (ROV), an autonomous underwater vehicle (AUV), in situ oxygen profilers and experiment chambers, in situ pumps, and 50 inter-calibrated hydro-acoustic and optical sensors for measuring the suspended sediment concentrations and particle sizes.