The mining of the deep seabed, at depths of 2,000 metres and greater, is increasingly being considered as a potential solution to the expected global shortage of so-called ‘transition-critical’ raw materials needed for the manufacture of batteries and other technologies that will be key to meeting targets to reduce greenhouse gas emissions. Minerals like lithium, nickel, cobalt, manganese and graphite are essential components of most batteries used today. Rare earth elements (REEs) are needed for a range of technologies, including the engines of wind turbines. Demand for these minerals is increasing and will continue to do so in the race to meet net zero targets. The construction of an onshore wind farm, for example, requires nine times more mineral resources than a gas-fired power plant.

The mineral deposits of transition-critical materials on land are highly concentrated in just a few countries, making their global availability dependent on trade relationships and vulnerable to supply disruptions that may result from export restrictions, political instability or natural disasters. G7 ministers have acknowledged the need to counter the geopolitical risks associated with these transition-critical minerals, diversify supply sources and have stated their intention to engage with key stakeholders on deep sea mining. The opportunities that deep-sea mining offers in the provision of transition-critical materials have been emphasised by a number of industry representatives, research institutes, specialised companies and governments, reflecting the fast-growing interest.

What mineral sources are there in the deep sea and how can they be accessed?

Supporters of deep sea mining are particularly interested in ‘polymetallic nodules’, which can be found across vast areas of the abyssal plain (the deepest and flattest part of the ocean floor) at depths of 3,500 to 6,000 metres. Unlike terrestrial mineral deposits, one single deposit of nodules can provide access to multiple commodities. For example, one of four key regions, the Clarion–Clipperton Zone (CCZ), which lies beneath the central Pacific Ocean, is estimated to hold 21.1 billion dry tons of nodules containing manganese, nickel, copper and cobalt. Other sources of mineral deposits include: polymetallic sulphides, which can be mined around hydrothermal vents on the ocean floor; and ferromanganese crust, which is rich in cobalt and found on underwater mountain ranges. However, the polymetallic nodules are attracting the most interest for mining.

Nodules are loosely scattered on the seafloor, making them relatively easy to collect with underwater dredging machines, which are submerged and driven along the ocean floor. They extract the nodules by sucking them up through a tube and pipe them to a vessel on the ocean surface.

What are the environmental impacts of seabed mining?

The deep sea is known to be the largest habitat for life on the planet, home to a vast variety of unique species and ecosystems and thus a wealth of biodiversity. Compared with on-land ecosystems, the deep sea is still poorly understood, with its high pressure, darkness and perpetual cold temperatures making this a challenging environment to access and study. As such it has been referred to as Earth’s ‘final frontier’. However, projects are underway to shine a light on deep sea ecosystems in response to discoveries of mineral deposits and the emerging commercial exploitation of deep sea exploration.

Studies have suggested that the nodules and sediment contribute to a high habitat heterogeneity, which is the driving force of the CCZ’s megafaunal diversity. Research published in May 2023 identified over 5,000 species not previously known to science in this region.

While the full extent of the impacts of deep-sea mining on this highly biodiverse environment is still uncertain, the following key impact drivers are already known:

Habitat removal: Probably the most obvious environmental impact of deep-sea mining is the removal of the nodules themselves, which likely changes the sediment’s geochemistry and causes many organisms to lose their habitat. As nodules grow only a few millimetres every million years, it is unlikely that certain species, especially sessile animals (those which attach themselves to rocks) would be able to recover from their removal.  

Sediment and plume disturbances: The extent to which plumes of fine sediment materials impact species abundance and diversity is not clear, despite much research and modelling, and largely depends on sediment resettlement patterns. However, it is known that the dispersion of fine sediments creates similar effects to air pollution on land, such as barriers to mobility and visualisation for organisms, likely decreasing their reproduction rates.

Water discharges and toxic compounds: Discharged dredging spoils, marine litter and cooling or ballast waters carried by marine vessels associated with mining all have impacts on ocean ecosystems. The mining process may also release toxic compounds that naturally occur on the ocean floor. During the extraction of nodules, streams of water are discharged at the seabed which can increase surrounding seawater temperatures and reduce oxygen levels. On the ocean surface, the minerals are separated, and dissolved metals and sediment are released back into the ocean. Midwater ecosystems, which play a key role in connecting the deep sea with shallow ecosystems, and in absorbing carbon from the atmosphere, are negatively affected by these discharges. For example, zooplanktonic species are destroyed and heavy metals are introduced into the ecosystem – which may contaminate seafood. As the ocean ecosystems between 200 and 1,000 metres’ depth are home to the largest stocks of fish, potential disruptions to sources of food for fish may pose a threat to over three billion people that rely on fish as a source of protein.

Noise pollution: Marine vessels generate noise on the ocean surface, while mining vehicles and related equipment generate noise at the deep-sea level. In the ocean environment sounds travel faster than through air and across huge distances, providing an effective communication medium for its inhabitants, which are highly sensitive to acoustic changes. They can thus be easily disrupted by anthropogenic noise which interferes with communication between marine mammals, for example.

Light pollution: Only about 1% of sunlight reaches ocean depths of 200 metres. Consequently, many organisms are adapted to the darkness and have reduced visual capacities. The artificial light used to control mining vehicles’ cameras and monitor the sites disturbs organisms with highly sensitive vision.

Economic disruption: Especially in small island developing states and other coastal countries, a significant number of economic sectors depend on marine ecosystems, including fisheries, aquaculture and mariculture, maritime transport and tourism. Marine ecosystems provide humans with important ‘ecosystem services’ such as a regulated climate, storm protection, and food and jobs for a significant proportion of the population. The environmental impacts of mining the oceans for transition-critical minerals could cause serious disruption to those value chains and create conflict between different interest groups – including at the international level, due to the transboundary nature of marine activities.

What is the current status of deep-sea mining and its governance?

Most deep-sea mining is expected to take place in international waters, i.e. beyond the territorial waters of any country, where governance and enforcement of regulation depend on international agreements – and are currently lacking when it comes to deep-sea mining. Since its formation in 1994, following enforcement of the UN Convention on the Law of the Sea (UNCLOS), the International Seabed Authority (ISA) has had responsibility for developing rules, regulations and procedures associated with seabed minerals and the authority to oversee related developments in international waters. To date, the ISA has granted over 30 contracts allowing the exploration of around 1.5 million km2 of ocean floor for deep-sea mining.

The ISA has been under pressure to finalise and adopt regulations on deep-sea mining since June 2021 when Nauru, an island state in Micronesia, triggered the so called ‘two-year rule’, requiring the ISA to complete the adoption of guidelines within two years. This period has now ended and, as of July 2023, no guidelines have been adopted. Instead, the Council of the ISA published a roadmap on how it intends to draft exploitation regulations, with their planned adoption in 2025. With the passing of the two-year rule, applications to exploit minerals can now be submitted to the ISA which has the authority to provisionally approve them, even without guidelines in place. The company most likely to lodge an application is Canada-based TMC, whose CEO has stated it would be ready to file an application in the second half of 2023.

How are different parties responding to the possibility of deep-sea mining?

Several countries support a moratorium. These include the Government of Palau, who with Fiji, the Federated States of Micronesia and Samoa launched the Alliance of Countries Calling for a Deep-Sea Mining Moratorium in June 2022; Canada, New Zealand, Switzerland and French Polynesia. In France, after President Macron announced his support for the prohibition of deep seabed exploitation, the French Parliament voted in favour of a moratorium, banning mining until sufficient scientific knowledge exists to assure that it can go ahead without causing harm. A group including Chile, Ecuador, Costa Rica, Vanuatu, Germany, Finland, Spain and Ireland have called for a ‘precautionary pause’ of around 15 years to provide more time for scientific research and to establish environmental standards on deep-sea mining.

The growing demand for transition-critical minerals needed to achieve net zero, combined with the environmental, social, geopolitical and supply-related challenges associated with further exploitation of terrestrial sources, means that the debate around deep-sea mining will continue for the foreseeable future.

This Explainer was written by Lea Reitmeier with review by Simon Dikau, Darian McBain and Francisco de Melo Viríssimo.

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