What is deep sea mining?

Deep seabed mining is the extension of terrestrial and shallow-water mining activities in the deep ocean in the quest for minerals. It requires new technologies and approaches and new scientific knowledge, most of which have yet to be acquired and developed. 

There is widespread concern about the impact deep seabed mining will have on the ecosystems and habitats of the deep and how the practice can be managed. The practice is at an early stage – highly speculative and experimental. Consequently, the nature of the adverse impacts on deep sea ecosystems remains unknown. But existing information has led scientists to warn that deep seabed mining could affect hundreds of thousands of square kilometers of seabed, and release both highly toxic chemicals and vast sediment plumes.1

The pace of development is breathtaking. A new breed of specialized mining firm is poised to dive deep in its quest for rich sources of minerals, including valuable metals and rare earth elements (REEs) for booming high tech and renewable energy industries.

It is vital that this quest for wealth is tempered by a strong set of mechanisms and controls which protect the marine environment and its biodiversity, ensure that extreme caution is taken, and allow the fair allocation of gains from the global commons for both current and future generations. Potential for mineral wealth in the deep ocean was identified as early as the 1960s. However, attempts to mine have been unsuccessful so far, as the reserves have proved too expensive to get to and difficult to mine. It is only very recently, as technological advancement has been matched by escalating commodity prices and demand, that the highly speculative practice has begun to be considered economically viable by some companies, and territorially important by some countries. Currently none of the main terrestrial mining companies or investors are involved in this prospecting.

Demand and Supply

Since the turn of the century, several factors have converged to propel deep seabed mining from a much-discussed concept towards becoming a practical reality.A major impetus for exploiting minerals in the deep sea has been increasing global demand for copper, cobalt, nickel, lithium, silver and other rare earth and specialty metals. This is partly being driven by the growth of renewable energy technologies. The metals are needed for rechargeable batteries, solar photovoltaic generators and wind power plants. This increase in demand has coincided with an observed decline in the quality of ores derived from terrestrial mines around the world.

Correlated with these market factors is a growing push in many countries to ensure a secure supply of such raw materials in the longer term.

On the supply side, huge technological advances – especially in the offshore oil and gas industries, which have been moving into ever deeper waters – have meant that many of the technical challenges posed by mineral extraction in the deep sea can now be overcome.This combination of perceived economic viability and technological feasibility has spurred a surge in interest displayed by both countries and private companies in developing the seabed-mining industry. However, an authoritative report from the Institute for Sustainable Futures has said that this demand can be met without plundering the ocean.

The report Renewable Energy and Deep Sea Mining: Supply, Demand and Scenarios, published in July 2016, found that projected demand for silver and lithium to 2050 will take up just 35% of known terrestrial resources, and demand for other metals – copper, cobalt, nickel, specialty and rare earth metals – represents less than 5% of existing resources. Further, although production of silver, lithium and some rare earth metals will need to increase, other strategies such as increased recycling have an important contribution to make.

The report concludes: “Even with the projected very high demand growth rates under the most ambitious energy scenarios, the projected increase in cumulative demand – all within the range of known terrestrial resources – does not require deep sea mining activity.”


Vast expanses of the Pacific, Atlantic, and Southern Indian Ocean seabed are slated for mining. Nearly 600,000 km2 of Pacific Ocean (almost the size of France) have been granted mining leases or exploration contracts, including sites in Papua New Guinea, Solomon Islands, Fiji, Vanuatu, Tonga and the international seabed Area between Hawaii and Mexico.

Globally the ISA has issued 27 exploration leases for polymetallic nodules, polymetallic sulphides and cobalt-rich ferromanganese crusts in the deep seabed. These leases cover a total of approximately 2 million km2 of seabed,[i]creating the largest mining operation the planet has ever seen and dwarfing anything comparable on land.
In total, around 7.5% of the global mid-ocean ridge – some 6,000km (250 times longer than Manhattan) – is now being explored for its mineral wealth. This is the geological backbone of the ocean.2

By one estimate 5% of the world’s minerals – including cobalt, copper and zinc – could come from the ocean floor as early as 2020, rising to 10% by 2030. According to these projections, global annual turnover of marine mineral mining could grow from virtually nothing to €5 billion in the next 10 years and up to €10 billion by 2030.3

Types of deep seabed mining proposed

There are currently three types of mineral of interest to prospectors in the deep ocean.

Polymetallic manganese nodules

Manganese nodules are mineral precipitates of manganese and iron oxides. They occur over extensive areas of abyssal plains at depths of 4,000–6,500 meters and grow extremely slowly – 2 or 3cm every million years. Nodules contain nickel, copper and cobalt, as well as traces of other metals (notably REEs) that are important to high-tech industries.
Various forms of mineral extraction are being considered for full-scale operations but many are variants on the hydraulic suction system. Hydraulic suction mining vacuums up the nodules for transfer to the mining vessel and then a second pipe may return tailings (usually fine particles) to the seabed.

The nodules provide a substrate for a variety of suspension feeders and creatures that live on or just below the surface and which are wholly dependent on nodules for their survival. These sediment communities are known to differ greatly between areas and have extremely slow restoration rates. In common with most deep sea life forms, little is known about how much space these colonies and species need to survive.4

Mining manganese nodules will occur over large areas and it is possible that all living organisms on the seafloor and below the surface will be destroyed, with adverse impacts spreading to the surrounding areas through sediment plumes. This habitat is poorly adapted to cope with disturbance.5 Experiments carried out in the Peru basin and the Clarion Clipperton Zone in the Southwest Pacific found that even though mobile species may return after mining disturbance has ended, sessile species do not recover.6

Under current mining scenarios, this process represents a major environmental impact.

Cobalt-rich ferromanganese crusts

Cobalt precipitates onto rock surfaces in the deep ocean that are free of sediment (mainly seamounts). Layers build at such a slow rate that it takes one million years for a crust to grow between 1 and 5mm, less than the thickness of an iPhone. This is one of the slowest natural processes on Earth.

Crusts of economic interest occur at depths of 800–2,500 meters on seamounts, mainly in the Pacific Ocean.

Technologically, the mining of cobalt crusts is more complex than manganese nodules. Environmentally, it is even more damaging. Cobalt-rich crust mining involves the removal of the top layer of crust on the flanks and summit of a seamount to a depth of 5–8cm (or 10–16 million years’ worth of growth). This is home to all the highly endemic species associated with seamounts and the other species dependent upon them.

As yet there is no lead technology for cobalt-rich crust mining but one method under consideration involves an enormous bottom crawling vehicle, attached to a surface vessel, which uses articulated cutters to fragment the crusts. Others envisage water-jet stripping, chemical leaching or sonic separation of crusts from rock.7

In addition to the massive destruction involved in removing the top crust, sediment plumes are likely to impact on suspension feeders such as sponges and corals beyond the impact site.Many seamounts are larger than mountains on land, with some dwarfing Mount Everest. They obstruct current flow, which results in strong eddies and upwelling, increasing primary biological productivity. The effects of these currents are greatest at the outer rim around the summit region, where the thickest crusts are found.

The seamounts are biodiversity hot spots in the ocean, supporting complex ecosystems from their surface to their base. They are also known to be a stopping point for migratory species, which use them as the equivalent of a motorway rest station. Any disturbance to such a finely balanced and slow-growing ecosystem is of concern, but the sheer scale of the mining envisaged could be sufficient to tip whole ecosystems into danger. Many seamounts have already been damaged by bottom trawling and thus have lower resilience and need to be protected from further damage.8

Polymetallic sulphides

Deep sea hydrothermal vents – now thought to be the cradle for all life on Earth – are found along mid-ocean ridges and back-arc basins and support some of the rarest and most unique ecological communities known to science. Called “black-smoker complexes”, the vents are outgrowths of minerals, formed while new oceanic crust is created where tectonic plates converge or move apart.Organisms at vent sites do not derive their energy from light but from sulphide chemicals in hot (350OC) mineralized vent fluids. They are unlike any other life form on the planet. Most species discovered at vents are new to science, and the vents support communities with extremely high biomass relative to other deep sea habitats.

The first commercial operator to explore for polymetallic sulphide deposits is Nautilus Minerals, which has commenced exploration in the exclusive economic zones (an area surrounding coastal nations, stretching out 200 nautical miles or 370 kilometers) of Papua New Guinea, Fiji and Tonga (covering an area roughly the size of the UK). This has been negotiated outside the auspices of the International Seabed Authority (ISA), directly with the national government of each country. For this work, Nautilus has developed a huge robotic machine called the “bulk cutter”, which weighs 310 tons (the equivalent of over 40 London buses) and is roughly as large as a medium-sized house. Although mining systems are still in development, they seem likely to be based around continuous-recovery systems using rotating cutter heads.9

Mining of hydrothermal vents would destroy an extensive area of vent habitat, including thousands of vent chimneys, killing virtually all the attached organisms. While more sea life is known to be attached to active hydrothermal vents, even the destruction of inactive hydrothermal vents will entail widespread habitat removal and destruction of species. The extent of the impacts to vents and other seafloor habitats mined will inevitably be severe at the site. Mining is also expected to alter venting frequency where active hydrothermal vents are affected as well as characteristics on surrounding seafloor areas, affecting ecological communities beyond the mined site. Life forms destroyed may well be endemic, meaning that mining may destroy species before they are even identified.

The uniqueness and fragility of this geographically fragmented ecosystem is of interest to scientists, is a potential source of new life-saving medicines, and may hold many secrets about evolution and adaptation of life on Earth.


1. http://www.eu-midas.net/science
2. http://www.bbc.co.uk/news/science-environment-28442640
3. http://na.unep.net/geas/getUNEPPageWithArticleIDScript.php?article_id=11
4. http://www.eu-midas.net/science/nodules
5. Stoyanova, 2012; Zhou, 2007.
6. Kaneko et al., 1997; ISA, 1999; Thiel et al., 2001; Bluhm, 2001.
7. https://www.isa.org.jm/files/documents/EN/Brochures/ENG9.pdf
8. http://na.unep.net/geas/getUNEPPageWithArticleIDScript.php?article_id=112
9. https://www.isa.org.jm/files/documents/EN/Brochures/ENG8.pdf