In-situ environmental monitoring for deep-sea polymetallic nodule mining: Status, challenges, and future directions

The prospective mining of deep-sea polymetallic nodules, a source of strategic critical metals, could cause irreversible damage to fragile deep-sea ecosystems, sparking global scientific, political, and ethical controversies. Consequently, establishing a scientific, credible, and efficient in-situ environmental monitoring system is a core prerequisite for achieving sustainable resource development and effective environmental regulation. This paper reviews the latest progress in in-situ environmental monitoring for polymetallic nodule mining (PNM). First, integrating future commercial mining workflows with current pilot-scale engineering practices, this paper outlines the multi-source environmental disturbances of PNM. The review then analyses impact mechanisms and monitoring strategies for five key areas: physical oceanography, marine chemistry, geology, marine biology, and sediment plumes. Finally, by assessing typical international monitoring campaigns, the paper distils key scientific findings and identifies core challenges. In-situ monitoring indicates that under the specific environmental conditions of PNM areas, mining plumes primarily propagate as near-bottom gravity currents, and that damage to benthic habitats can persist for decades. However, significant technical bottlenecks and scientific uncertainties remain in quantifying micro-scale processes, conducting continuous long-term observation of ecological recovery, and enabling real-time fusion of multi-platform data.