More than four decades after a commercial mining trial left 100-tonne machine tracks on the floor of the Pacific Ocean, researchers returning to the Clarion-Clipperton Zone in 2023 discovered that the seabed environment and its organic food supplies have failed to recover from the industrial disturbance.
Deep beneath the central Pacific, where industrial machinery churned through the sediment in 1979, the scars left behind remain starkly visible. A research team inspecting the site found that tracks carved by a 100-tonne mining machine operated by the Ocean Minerals Company have barely changed over the span of 44 years. At depths hovering around 4,800 metres, sparse animal populations and sluggish sediment movement mean natural restorative processes unfold at a glacial pace.
The investigation formed part of the UK Natural Environment Research Council-funded SMARTEX project, which brings together scientists from the National Oceanography Centre, the Natural History Museum, the University of Liverpool, Eckerd College, and institutions in Denmark. Armed with still and video imagery alongside sediment cores collected during a month-long expedition aboard the Royal Research Ship James Cook, the team set out to measure how organic matter recovered within and around the historic disturbance zones.
Persistent Scars and Depleted Organic Food Web Components
The study, published in Elementa: Science of the Anthropocene, revealed that the physical furrows left by heavy equipment created an approximately 8-metre-wide strip of seafloor stripped of its mineral deposits. Within these tracks, particulate organic matter—vital nutritional debris containing carbon, nitrogen, and omega-3 fatty acids that supports growth and reproduction for benthic organisms—remained noticeably lower in both quantity and quality.
Marine biologist Dr Rachel Jeffreys of the University of Liverpool, lead author of the research, emphasized the long-term reach of those initial industrial trials.
This localized food depletion directly impacts the abundance of life. While smaller mobile creatures and single-celled organisms like xenophyophores have returned in numbers comparable to undisturbed control sites, larger organisms remain scarce. Sessile species that depend entirely on the solid surface of polymetallic nodules—such as deep-sea corals and sponges—cannot simply relocate, leaving entire biological niches empty where the mineral-rich rocks were removed.
Benthic Fauna Keep Nodules Exposed on the Abyssal Plain
A companion line of research co-led by the National Oceanography Centre and the Institute of Marine Sciences in Barcelona has uncovered a vital maintenance mechanism that governs these abyssal plains. For decades, scientists puzzled over how polymetallic nodules—potato-sized mineral deposits rich in nickel, cobalt, and copper—remained exposed on the seabed rather than getting buried beneath continuous layers of settling marine mud.
Time-lapse photography surveys documented mobile benthic fauna, including sea cucumbers, sea urchins, and sea snails, actively clearing sediment from the tops of the nodules.
Erik Simon-Lledó, senior author of the ICM-CSIC study, warned that industrial extraction threatens this delicate biological maintenance loop.
Abyssal nodule mining could trigger cascading ecological impacts that had not been considered until now. By reducing the mobile fauna, a functional mechanism keeping the hard substrate exposed would be affected making it harder for species like corals and sponges to recolonize the environment, aggravating the already known effects of mining on the rich biodiversity of these ecosystems.
Commercial Momentum Versus Economic and Environmental Risks
These empirical findings emerge as proposals to advance commercial deep-sea mining gather momentum across international waters. The Clarion-Clipperton Zone, stretching between Hawaii and Mexico, has drawn intense interest from companies seeking critical metals for rechargeable batteries and touch screens.
At the test site itself, researchers noted one relative silver lining: sediment plumes generated by the machinery appeared to have limited long-term physical effects compared to the direct removal of nodules and physical track carving. However, scientists caution that this distinction does not mean plumes are harmless across every deep-sea environment. With commercial regulations and protected area designations currently under debate, researchers stress that long-term monitoring of organic matter availability and ecosystem engineers must form a core pillar of any future management framework in the deep ocean.