• Deep-sea mining is the process of retrieving mineral deposits from the deep sea – the area of the ocean below 200 m.
• Depleting terrestrial deposits and rising demand for metals are stimulating interest in the deep sea, with commercial mining imminent.
• The scraping of the sea floor and pollution from mining processes can wipe out entire species – many yet to be discovered.
• Environmental impact assessments, effective regulation and mitigation strategies are needed to limit the impacts of deep-sea mining.
• Comprehensive baseline studies are needed to improve our understanding of the deep sea.
The seafloor contains an extensive array of geological features. These include abyssal plains 3,500–6,500 m below the sea surface, volcanic underwater mountains known as seamounts, hydrothermal vents with bursting water heated by volcanic activity, and deep trenches such as the Mariana Trench, which at almost 11,000 m is the greatest depth registered in the ocean. These remote areas support species that are uniquely adapted to harsh conditions such as lack of sunlight and high pressure. Many of these species are unknown to science.
As the deep sea remains understudied and poorly understood, there are many gaps in our understanding of its biodiversity and ecosystems. This makes it difficult to thoroughly assess the potential impacts of deep-sea mining and to put in place adequate safeguards to protect the marine environment.
Based on current knowledge of the deep sea, the following impacts of mining activities could affect its biodiversity and ecosystems:
Disturbance of the seafloor
The scraping of the ocean floor by machines can alter or destroy deep-sea habitats, leading to the loss of species and fragmentation or loss of ecosystem structure and function. Many species living in the deep sea are endemic – meaning they do not occur anywhere else on the planet – and physical disturbances in just one mining site can possibly wipe out an entire species. This is one of the biggest potential impacts from deep-sea mining.
Some forms of deep-sea mining will stir up fine sediments on the seafloor consisting of silt, clay and the remains of microorganisms, creating plumes of suspended particles. It is unclear how far these particles may disperse beyond the mining area, how long it would take for them to resettle on the seafloor, and to what extent they may affect ecosystems and species, for instance by smothering animals or harming filter-feeding species that depend on clear, clean water to feed, such as krill and whale sharks.
Species such as whales, tuna and sharks could be affected by noise, vibrations and light pollution caused by mining equipment and surface vessels, as well as potential leaks and spills of fuel and toxic products.