Monitoring Strategies of Suspended Matter after Natural and Deep-Sea Mining Disturbances

Abstract

The world’s oceans are increasingly under pressure from human activities, leading to warming and acidification of ocean waters, overexploitation of living resources, and uncontrolled dispersion of plastic litter and other pollutants. The advance of deep-sea mining poses yet another threat, especially to the unique, vulnerable, and largely unknown deep-sea life. The excavation of metal-rich mineral deposits from the deep-sea bed will not only remove hard substrate which deep-sea fauna like sponges and corals need for settlement; it will also produce sediment plumes which will be dispersed by currents, and which are expected to affect deep-sea life over a much wider area than the actually mined area. If deep-sea mining will be given green light, strict monitoring of these sediment plumes will be needed to ensure that the dispersal of sediment plumes and concentrations of suspended particulate matter (SPM) therein will not exceed prescribed thresholds. In my PhD research I have explored strategies for effective monitoring of sediment plumes produced by deep-sea mining, with a focus on different sensor types that can be used for measuring SPM and how these sensors can best be deployed in monitoring. Field experiments in which the performance of commonly used turbidity sensors was tested in different setups and were carried out in the Whittard Canyon and the Rainbow hydrothermal vent field in the Atlantic Ocean, where enhanced suspended particle concentrations occur naturally, thereby serving as “natural laboratories”, and in the Mediterranean Sea offshore southern Spain and the Clarion-Clipperton Zone in the Pacific Ocean, where sediment plumes were produced artificially.