Deep sea mining for rare metals impacts marine life for decades, scientists say

Marine life in the deep ocean can take decades to recover from the impact of deep-sea mining for rare metals, new research shows.

A study published in the journal Nature found that the site of a deep-sea mining test in 1979 in the North Pacific still showed lower levels of biodiversity – species variety – than neighbouring undisturbed sites 44 years later.

The research was conducted in 2023 and 2024 5,000m below the surface in the Pacific Ocean in the Clarion–Clipperton zone. This is roughly halfway between Mexico and Hawaii and is a vast, flat and deep region of the ocean floor known as an ‘abyssal plain.’

Scientists at the National Oceanography Centre in Southampton led the research as part of a consortium that includes the Natural History Museum in London, British Geological Survey and Heriot-Watt University in Edinburgh, the Joint Nature Conservation Committee, the Scottish Association for Marine Science in Oban, Argyll, the University of Liverpool, University of Plymouth and University of Southampton.

The partners are part of Seabed Mining and Resilience to Experimental Impact (SMARTEX), a research project funded by UK Natural Environment Research Council. SMARTEX was set up to determine the ecological impact in the central Pacific Ocean of deep-sea mining for mineral deposits known as nodules that contain rare metals like cobalt, manganese and nickel, which are critical elements in electric car batteries and other electronic devices.

Dr Mark Hartl, a marine biologist at Heriot-Watt University who specialises in ecotoxicology – how organisms are exposed to and impacted by pollutants – is part of the SMARTEX consortium and co-author of the research.

He explained: “These nodules are potato-sized mineral deposits that have built up in layers over thousands of years. Mining companies want to mine these for critical metals like cobalt and nickel. But there are so many unanswered questions. For example, we know the nodules produce oxygen. If they’re removed, will that reduce the amount of oxygen in the deep sea and affect the organisms that live there? What is the effect of animal exposure to metal-containing sediment plumes churned up during the mining process? These are some of the questions we’re trying to answer.”

Dr Hartl’s role involved researching how deep-sea organisms are affected by sediment exposure and associated stress, to help quantify the less obvious impacts of deep-sea mining. As part of this, he developed a procedure to measure how mining could damage the DNA – the genes – of deep-sea fish. This is published in the journal Deep Sea Research.

“This has never been done before,” Dr Hartl said, “So we had no baseline data to compare any effects of mining against.  We are currently optimising tests for other signs of stress applicable to the deep sea.”

More than 21 billion tonnes of nodules are estimated to lie on the seabed of the Clarion-Clipperton Zone, which spans more than 6 million square kilometres – about 25 times the size of the UK.

These nodule fields sustain “highly specialised animal and microbial communities,” the researchers say. These include giant single-celled organisms with chalky shells (called ‘foraminifera’); highly specialised sea cucumbers and fish – and many species that rely on the nodules as the only hard surface to settle on.

The researchers studied an area on the ocean floor where a 14 metre long experimental mining machine was deployed in March 1979. This mined an unknown quantity of nodules over the four days, using a mechanical rotating seabed rake that picked up nodules and transferred them via a conveyor to a crusher.

The scientists conclude that, four decades after this mining test, “the biological impacts in many groups of organisms are persistent,” although some species have started to recover.

The physical signs of the test are also still visible, including areas of the seabed that have been stripped of nodules, and visible track marks from the mining vehicle.

Research lead author and expedition leader, Professor Daniel Jones of the National Oceanography Centre explained: “To tackle the crucial question of recovery from deep-sea mining, we need first to look to the past and use old mining tests to help understand long-term impacts. Forty four years later, the mining tracks themselves look very similar to when they were first made, with an 8-metre-wide strip of seabed cleared of nodules and two large furrows in the seafloor where the machine passed. The numbers of many animals were reduced within the tracks but we did see some of the first signs of biological recovery.”

Co-author, Dr Adrian Glover, from the Natural History Museum, said: "General ecological theory will predict that following disturbance, any ecosystem will go through a series of successional stages of recolonisation and growth. However, until this study, we had no idea of the timescales of this critical process in the deep-sea mining regions, or how different parts of the community respond in different ways.

“Our results don’t provide an answer to whether deep-sea mining is societally acceptable, but they do provide the data needed to make better informed policy decisions such as the creation and refinement of protected regions and how we would monitor future impacts.”

Deep-sea mining is currently prohibited under an international moratorium – suspension – while the International Seabed Authority (ISA) – which regulates and manages all mineral-related activities on the international seabed – develops the legal, financial, and environmental framework to underpin any potential full commercial exploitation, when it occurs. A key question in this decision, is whether deep-sea ecosystems can recover from mining disturbances, the National Oceanography Centre says.

It adds that deep-sea mining is increasingly being considered as a potential solution to supply the crucial metals required for advancing global technology and driving the transition to a net zero energy future.

In their Nature paper, the researchers say nodule mining is expected to cause “immediate impacts” to the seabed surface and habitat in the path of collector vehicles. This includes mechanical disturbance, including the removal of hard surface spaces for species to live below the seabed and the compacting of sediment. Another impact is the creation of sediment plumes which could have “significant impacts on ecosystems” beyond the immediate mined areas, the researchers say.

The study is entitled, Long-term impact and biological recovery in a deep-sea mining track after 44 years.