In places, the deep ocean seabed is scattered with ancient rocks, each about the size of a closed fist, called ‘polymetallic nodules’. Elsewhere, along active and inactive hydrothermal vents and the deep ocean ridges, volcanic arcs, and tectonic plate boundaries, and on the flanks of seamounts, lie other types of mineral-rich deposits containing high-demand minerals.  

Deep sea mining is a new frontier in mineral extraction, with potentially significant implications for industry and the global economy, and important environmental and societal considerations. Professor of Mechanical Engineering Thomas Peacock and his team in MIT’s Environmental Dynamics Laboratory (ENDLab) have been studying the potential biological and environmental impacts of deep sea mining in a region of the Pacific Ocean known as the Clarion Clipperton Zone (CCZ), where polymetallic nodules abound. To assess the environmental impact of harvesting those materials, the team is developing cutting-edge monitoring programmes, novel sensors and modelling tools.

In deep sea nodule mining, vehicles collect nodules from the ocean floor and convey them back to a vessel above. After the critical materials are collected on the vessel, some leftover sediment may be returned to the deepwater column. The resulting sediment plumes, and their potential impacts, are a key focus of the team’s work.

‘We are studying the form of suspended sediment from deep sea mining operations, testing a new sensor for sediment and another new sensor for turbulence, studying the initial phases of the sediment plume development, and analysing data from the 2021 and 2022 technology trials in the Pacific Ocean,’ explains Peacock.

MIT researchers collected polymetallic nodules from the floor of the Pacific Ocean  

Photo: (video still) MIT Mechanical Engineering 

A 2022 study conducted in the CCZ investigated the dynamics of sediment plumes near a deep seabed polymetallic nodule mining vehicle. The experiments revealed most of the released sediment-laden water, between 92–98%, stayed close to the seabed floor, spreading laterally. The results suggest that turbidity current dynamics set the fraction of sediment that remains suspended in the water, along with the scale of the subsequent ambient sediment plume. The implications of the process, which had been previously overlooked, are substantial for plume modelling and informative for environmental impact statements, says Peacock.

‘New model breakthroughs can help us make increasingly trustworthy predictions,’ he continues.

The team also contributed to a recent study published in the journal Nature, which showed that sediment deposited away from a test mining site gets cleared away, most likely by ocean currents.  

They also reported on any observed biological recovery. Researchers observed a site four decades after a nodule test mining experiment. Although biological impacts in many groups of organisms were present, populations of several organisms, including sediment macrofauna, mobile deposit feeders, and even large-sized sessile fauna (animals that are attached to a substrate and do not move from place to place), had begun to reestablish despite persistent physical changes at the seafloor. The study was led by the National Oceanography Centre in the UK.

‘A great deal has been learned about the fluid mechanics of deep sea mining, in particular when it comes to deep sea mining sediment plumes,’ says Peacock. He believes his team’s work is setting new standards for in-situ monitoring of suspended sediment properties and for how to interpret field data from recent technical trials.