Long-Term Ecological Impacts of Deep-Sea Mining in the Clarion Clipperton Zone

By Dr. Noopur JainReviewed by Laura ThomsonApr 4 2025

In a recent article published in the journal Nature, researchers examined the long-term ecological effects of seabed mining by analyzing a historic mining test site from 1979. The rapid increase in deep-sea mining exploration, particularly in the Clarion Clipperton Zone (CCZ) of the Pacific Ocean, has raised concerns about the potential environmental impacts on unique abyssal ecosystems.

Researchers combined archival data from the Ocean Minerals Company (OMCO) with new field observations from 2023 to assess the extent of recovery in biological and physical parameters after 44 years. These findings are crucial for developing regulatory frameworks to balance resource extraction with biodiversity conservation.

Background

The CCZ is estimated to contain over 21 billion tons of polymetallic nodules, rich in valuable metals such as cobalt and nickel, making it a prime target for commercial mining. However, this region also supports highly specialized deep-sea communities characterized by high biodiversity but low abundance and biomass. Mining activities pose significant threats, as collector vehicles disrupt the seabed, removing critical hard substratum habitats and compacting sediment. Additionally, mining generates sediment plumes that can spread over vast areas, altering biogeochemical conditions and increasing water turbidity.

Previous studies, including the DISCOL experiment in the Peru Basin, have shown that ecological impacts from seabed disturbances can persist for decades. However, these studies were conducted in areas with different environmental conditions from the CCZ, leaving critical knowledge gaps regarding long-term recovery potential in commercially viable mining regions. Given the scale of potential mining operations, with each covering approximately 400 km² per year for up to 20 years, cumulative impacts could be extensive. Understanding the resilience and recovery of abyssal ecosystems is vital for shaping effective environmental policies.

The Current Study

This study assessed the long-term ecological impacts of deep-sea mining by examining a historic mining disturbance site in the Clarion Clipperton Zone (CCZ). The site, disturbed in 1979 by the Ocean Minerals Company (OMCO) collector test, provided a unique opportunity to evaluate recovery patterns over 44 years. Researchers combined archival data, including location records and engineering details of the mining test, with recent field observations conducted in March 2023.

High-resolution imagery and sediment samples were collected from disturbed and undisturbed control areas to analyze the site. Seafloor characteristics were examined to assess physical changes, while macrofaunal and microbial communities were surveyed to determine biological recovery. The study focused on three key disturbance features: collector tracks, vehicle propulsion tracks, and sediment plumes. Physical alterations, species diversity, and organic matter distribution were compared between impacted and control regions to determine the extent of ecological succession.

Results and Discussion

The findings reveal that the mining disturbance remains evident after 44 years, with significant variations in recovery across different impact zones. The collector tracks, where sediment and nodules were removed, still exhibit lower organic carbon content than undisturbed areas. While sediment-dwelling macrofauna, including annelids and arthropods, show near-complete recovery in terms of density, nodule-dwelling organisms remain vulnerable due to partial or complete loss of their habitat. Sessile megafaunal organisms, such as sponges and corals, are largely absent in disturbed areas, with only a few individuals found on undisturbed nodules.

The vehicle propulsion tracks, which created deep furrows in the seabed, have undergone limited recovery. These areas continue to trap organic material and plastic debris, resulting in a distinct faunal composition dominated by echinoids and holothurians. However, biodiversity remains lower than in control areas.

The sediment plume, which spreads resuspended material beyond the direct mining tracks, does not show clear visual distinctions from control sites. This suggests that sediment redistribution and natural oceanographic processes have smoothed the impact over time. However, minor infill between nodules was detected, and some megafaunal densities were elevated in plume-affected areas, possibly due to organic material deposition.

The study demonstrates that while certain macrofaunal communities have shown resilience, sessile species and habitat-dependent organisms have not fully recovered. These results highlight the long-lasting consequences of deep-sea mining, underscoring the need for stringent environmental management strategies to mitigate future impacts.

Conclusion

This study provides valuable insights into the long-term ecological impacts of deep-sea mining disturbances in the Clarion Clipperton Zone (CCZ). Even after 44 years, the physical and biological effects of the OMCO mining test remain evident, highlighting the slow recovery of abyssal ecosystems. While sediment-dwelling macrofauna has largely regained their pre-disturbance densities, nodule-dependent species and sessile megafauna continue to show limited signs of recovery due to the permanent removal of hard substrate. The deep furrows created by vehicle propulsion remain largely unchanged, still affecting local biodiversity and sediment dynamics.

These findings underscore the prolonged consequences of mining-related disturbances and emphasize the importance of careful environmental regulation. Given the slow pace of recovery and the potential for cumulative impacts from multiple mining operations, stringent management strategies and further long-term studies are crucial to ensuring the protection of deep-sea biodiversity and ecosystem functions.