Monitoring discharge from deep-sea mining ships via optical satellite observations

Deep-sea mining may disturb the water column environment, including the surface water and deep-sea, and these disturbances should be carefully treated. Remote sensing provides high-resolution and accurate long-term observations in the area around deep-sea mining. Discharge from mining ships can be identified within few days from satellite observations based on changes in reflectance. A pioneer twomonth experimental deep-sea mining cruise was conducted by The Metal Company in the eastern Pacific Ocean from September 15 to November 17, 2022. A report from Greenpeace indicated incidents of surface discharge and leakage during this mining experiment. In this study, satellite observations captured a clear signal over the surface water from September 24 to October 28, indicating the location with discharged water from the mothership. The number of pixels where the potential discharged water was identified in the satellite imagery ranged from 4 to 13. The discharged water was transported by the combined effects of wind and currents, locating continuously to the downwind side of the mothership's mooring location. Remote sensing provides a timely and accurate monitoring system for tracking water discharge during deep-sea mining.