Deep sea mining: what are the environmental impacts?

Why is mining of the deep sea being proposed?

What could be mined in the deep sea?

The three main deposit types of interest, which form in different ways:

• Polymetallic nodules. The composition of nodules varies with location, but may contain manganese, nickel, copper, and cobalt in addition to rare-earth metals.
• Seafloor massive sulfides (SMS, associated with hydrothermal vents)). These are deposits that may contain copper, zinc, silver, and gold.
• Cobalt-rich crusts. These crusts contain cobalt, manganese, copper, and nickel.

Other deposits that could be exploited include rare earth element rich muds. Similar to nodules, SMS and crusts, these can take millions of years to form.  Please see POSTnote 508 Deep Sea Mining for more information.

Studies have identified where relevant deposits are likely to occur both within nation state’s exclusive economic zones and international seabed areas (figure 1).

Figure 1. Global distribution of polymetallic nodules (blue); polymetallic or seafloor massive sulfides (orange); and cobalt-rich ferromanganese crusts (yellow). (from © 2018 Miller, Thompson, Johnston and Santillo,  CC-BY 4.0).

Note: Waters 200 nautical miles from coastlines fall within national jurisdictions (exclusive economic zones, white) and beyond that they are governed through United Nations Convention on the Law of the Sea (UNCLOS, light blue).

How does deep sea mining work?

Technologies for DSM vary by mineral deposit type and are most developed for polymetallic nodules and SMS. They typically involve:

1. A sea floor tool to cut (crusts and sulphides) or collect (nodules), followed by transport of the deposit to a riser and lifting system.
2. A riser and lifting system through which the deposit is pumped to a surface support vessel.
3. A surface support vessel, which removes water from the deposit for transportation to a processing facility on land. The wastewater is pumped into the site of deposit collection or the water column.

These approaches are supported by other technologies such as underwater autonomous vehicles and artificial intelligence. Please see POSTnote 508 Deep Sea Mining for more information. Emerging approaches, such the use of novel collection technologies and new metal extraction methods have also been proposed.

Why is DSM being developed?

Forecasts suggest that demand is increasing for metals used in energy technologies and construction materials. For example, see the International Energy Agency clean energy forecasts under various scenarios. These forecasts are uncertain and could be affected by changes in policy or technologies. Demand drivers include economic factors and geostrategic factors, such as critical materials for defence technologies.

The need for DSM is contested. Some studies suggest land-based mineral reserves may be sufficient to meet demand, particularly for metals targeted by DSM. Others suggest demand cannot be met without expanding beyond these reserves.

The UK depends on international supplies of critical minerals. The 2025 UK Critical Minerals Strategy, Vision 2035, sets out measures to address challenges including:

• vulnerabilities in international supply chains
• increasing geopolitical tensions
• recovery and recycling of critical minerals through policies that promote circular economy practices

What are the possible environmental impacts of deep sea mining?

What are the possible impacts on marine species, habitats and ecology?

DSM could have several different environmental impacts (figure 2). However, these impacts are uncertain; there are major gaps in knowledge of deep sea ecology, impacts and recovery times because deep-sea habitats are remote and hard to access, and the depth makes sampling expensive. This makes environmental assessments, management and monitoring more difficult.

Impacts may differ in magnitude but could include:

• Destruction and disturbance of seabed habitat and organisms. Collector vehicles alter the seabed in their path, and they produce light, vibration, and noise pollution . For example, robotic collector vehicles remove the top layer of sediment along with nodules.
• Sediment plumes from the mining site or from associated sea vessels, which can extend beyond the mining area. These plumes can have wide-ranging effects on bottom-dwelling and midwater organisms, such as physical smothering and burial, clogging of respiratory, feeding, or olfactory organs and other physical damage. They may also reduce light penetration, water oxygenation and spread toxins, such as metal contaminants, and radioactivity.
• Destruction of the distinct microbial communities that have evolved around these deposits. These are a key part of global biogeochemical cycles for carbon, nitrogen and sulphur, but remain poorly understood. Mining may destroy the microbes’ habitats or bury them, impacts that may persist for decades.
• Disruption of the food web and ecological processes, as well as loss of fragile habitats and reduction in the diversity of species associated with them. For example, studies suggest the nutritionally poor particles in sediment plumes may also disrupt the marine food web that depends on organisms in the twilight zone between 200 and 1000 metres.
• Wider ecosystem effects arising from habitat or population fragmentation; disruption of species and genetic connectivity, such as larval dispersal.

Figure 2. The potential impacts of deep-sea mining on marine ecosystems (from © 2018 Miller, Thompson, Johnston and Santillo,  CC-BY 4.0)

A UK-based study has shown that, four decades after a nodule test mining, the biological and physical impacts persist, but that some organisms had begun to re-establish. However, knowledge of deep-sea ecosystems is generally poor, and around 90% of species in DSM areas are unknown. The response of species to mining at scale cannot be predicted but may include extinctions or irreversible ecosystem changes.

How is DSM regulated?

The International Seabed Authority

The International Seabed Authority (ISA) was established in 1994 under the UN Convention on the Law of the Sea (UNCLOS) to organise, regulate, and control all mineral-related activities in waters beyond the 200 NM national jurisdiction, also referred to as the High Seas.

Protection of ocean biodiversity is a central theme of the 2023 Marine Biological Diversity of Areas beyond National Jurisdiction Agreement under UNCLOS and with implications for ISA regulation.

The ISA ‘Mining Code’ consists of the exploration and exploitation regulations drafted in line with the advice of a Legal and Technical Commission. The ISA has issued 31 exploration contracts for 15 years length covering 1.5 million km² under seabed mineral exploration regulations.

Since July 2023, DSM applications could be submitted to the ISA, but DSM cannot be permitted until exploitation regulations are agreed. Academic commentators suggest over 30 major regulatory issues have yet to be resolved.

The ISA is required to protect the marine environment from the harmful effects of seabed mining activities, and to take a precautionary approach. There is no agreed definition yet of serious harm for the High Seas, and a lack of baseline data for most deep-sea environments creates challenges for assessing impacts.

The draft exploitation regulations now include an Environmental Compensation Fund system; a financial payment for harm or degradation by contractors and their sponsoring states.

US moves to unilaterally mine the High Seas

Seabed in the High Seas is ‘common heritage’ under UNCLOS, requiring equitable distribution of DSM proceeds. Exploitation is being proposed in both national and international waters.

The US has had legislation permitting US citizens to conduct DSM in areas outside its national jurisdiction since 1980 and has not ratified UNCLOS.  In 2025, the US Government issued an Executive Order to accelerate DSM, including in areas outside its national jurisdiction. The Metals Company (TMC) submitted applications in April 2025 under the legislation for exploration beyond US waters.

The proposal to undertake DSM in international waters on the basis of US permitting alone poses legal risks for mining companies. China currently holds five ISA contracts to explore for deep-sea minerals. Researchers raise concerns about the geopolitics of deep sea minerals, the implications for the environment and the ISA framework.

However, potential DSM locations are being explored within national waters (exclusive economic zones) including China, Japan, Norway, Papua New Guinea, Fiji, and the Cook Islands. China and the US are forming DSM alliances with other states, such as the Cook Islands.

UK Government DSM initiatives

The UK sponsors two ISA exploration licences and as an ISA member state contributes national expertise to regulations and decision making. 40 states have called for a moratorium on DSM. Positions on the moratorium differ. The UK supports one until there is sufficient scientific evidence on impacts.

The UK Deep-Sea Mining Environmental Science Network was established in 2024 to advise government, following an independent evidence review of DSM.

The UK Deep-Sea Mining Act 2014 amended the Deep Sea Mining (Temporary Provisions) Act 1981 to align with UNCLOS, licensing exploration and exploitation in ‘the Area’. The act mandates environmental assessments and liability provisions as well as allowing UK courts to enforce decisions made by the ISA Seabed Disputes Chamber.

Future considerations

Researchers suggest DSM viability depends on five interdependent challenges: technological readiness, environmental protection, economic feasibility, robust governance, and social acceptability.

A proposed Papua New Guinea DSM project (Solwara 1, see figure 1 for location), was unsuccessful because of community opposition, legal challenges, and major financial and corporate issues.

Litigation risks arise from countries or communities subject to environmental impacts, even from distant activities that disrupt natural resources or ways of life.

Studies conclude DSM will cause harm to poorly understood ecosystems, with a lack of data about the ecology of deep-sea species, gaps in understanding deep-sea ecological processes, their vulnerabilities, the ecosystem service benefits they provide to humans and developing indicators for these.

Researchers suggest regulatory thresholds or limits are developed for scientific, technical, legal and societal factors to balance precaution and risk.

These could inform adaptive management, where careful monitoring of the scale and extent of negative impacts informs ongoing understanding so that the regulatory approach being taken can be adjusted to address increasing risks.

By – https://post.parliament.uk/deep-sea-mining-what-are-the-environmental-impacts/