At the crossroads of ecological, geopolitical, technological and economic issues, the deep ocean is as intriguing as it is fascinating, as it is home to numerous resources, including abundant biodiversity. Its mineral wealth is highly coveted by the mining industry, which is currently stepping up its pressure. Scientific exploration is progressing but is still insufficient to ensure safeguards. Can we take the risk of causing irreversible damage before we know more?
By Marguerite Castel
Cover photo: Monster squid (Cerataspis monstrosus) photographed by the Victor 6000 ROV at the world’s deepest hydrothermal vent, Ashadze, at a depth of 4,200 metres. Ifremer, 2007. https://image.ifremer.fr/data/00569/68066/
At a meeting in March 2025, the 168 member states of the International Seabed Authority (ISA) once again examined a draft mining code to establish rules governing deep-sea mining. Created in 1994 under the auspices of the UN, the ISA is negotiating these future regulations for the industrial exploitation of seabed resources under its jurisdiction (international waters beyond the territorial waters of EEZs). These negotiations have not yet been concluded. They have been stalled for ten years. A new round of talks is scheduled for July 2025, with the aim of reaching an agreement.
This is especially true as pressure from the mining industry intensifies. Several companies that have invested in seabed exploration are coveting manganese, nickel, copper, cobalt and rare earths, most of whose deposits are located in the high seas. One example is the Canadian company The Metals Company (formerly Nautilus Minerals), which is stepping up its efforts. After announcing that it would submit its first application for an exploitation contract in June 2025 via its subsidiary Nori (Nauru Ocean Resources Inc.) to the AIFM, it revealed on 27 March that it was already in negotiations with the US administration to start exploitation with or without a mining code. Donald Trump is also trying to force the issue! On 24 April 2025, he signed an executive order aimed at accelerating the exploration and exploitation of the seabed, including in international waters.
This amounts to acting outside the legal framework (law of the sea) and circumventing the only competent authority on the high seas.
Only exploration is permitted and supervised
The ISA currently only authorises exploration to improve knowledge of the seabed: 31 contracts are currently underway, conducted by states with research centres or private companies. France is conducting two with Ifremer: in the Clarion-Clipperton zone in the North Pacific and on the Mid-Atlantic Ridge.
No exploitation licences have yet been granted pending the finalisation of the mining code.
Regulating underwater mining must also be consistent with the ISA’s other key mission: protecting the environment! Combining these two objectives seems paradoxical given the lack of scientific knowledge about these largely inaccessible and still largely unexplored ecosystems.
Regions where mining exploration is currently taking place in the high seas (the CCZ), in the Indian Ocean, on the Mid-Atlantic Ridge and in the north-western Pacific. Source @ISA
A moratorium of 10 to 15 years to learn and test
The scientific community and environmentalists fear that mining will be given the green light too soon. What would be the impact on biodiversity in the deep sea, on the Earth’s crust and on the very functioning of the ocean system? They argue that current knowledge is insufficient to determine the necessary safeguards. That is why 32 countries, including France (since January 2023), are calling for a moratorium to ban mining until its environmental safety has been proven.
On 31 March, at the SOS Ocean summit in Paris, palaeontologist and marine biologist Bruno David and oceanographer Françoise Gail unveiled the conclusions of their work on the consequences of launching deep-sea mining. Supported by a scientific committee of around 15 international researchers, they are calling for a moratorium ‘for ten to fifteen years’ to allow for a better understanding of how these ecosystems work.
‘It’s not just about protecting a sea urchin or a sea cucumber, however extraordinary they may be,’ says the former president of the National Museum of Natural History in Paris.
‘Deep-sea ecosystems are completely connected to the rest of the planet, and changing them could have repercussions on the Earth’s major biochemical cycles, including on the continents.’
The answers will be legal, but beyond that, the discovery of the deep sea represents a tremendous opportunity to advance our knowledge. Exploration has given rise to a wealth of scientific literature that can already inform international decision-making with objectivity.
Life in the extreme conditions of the deep sea!
The deep ocean beyond 1,000 metres represents 75% of the world’s ocean volume, or more than one billion km3. It lies beyond the continental shelf and includes the seabed, the ocean floor and their subsoil. It is the largest continuous biome (macro ecosystem) on Earth, but also the least explored! Today, 25% of the oceans have been mapped and 5% of the deep sea has been accurately explored, according to UNESCO.
This marine zone begins only 200 metres below the surface: at the limit of light penetration, where photosynthesis no longer occurs. Down to a depth of 1,000 metres is the twilight zone, followed by the aphotic zone, where it is dark and cold (2 to 3 degrees on average) and the pressure increases by one bar every 10 metres! The average depth is 3,800 metres and the maximum depth is 11,000 metres in the Mariana Trench (north-western Pacific Ocean).
These extreme conditions do not prevent a highly diverse range of life forms from existing: bacteria, shrimp, mussels, fish, corals, etc. 270,000 different species are now known, and the inventory is far from complete: an estimated 1 to 10 million species exist.
Drawing of mountains in the depths @ Julie Terrazoni
A mosaic of habitats
These various life forms are associated with specific habitats.
The majority are found in the abyssal plains, sandy-muddy bottoms that occupy 80% of the deep ocean, between 3,000 and 5,500 metres deep. Very small species, few in number but highly diverse, live there on particles falling from the surface.
In this vast abyssal space, the plains are punctuated by relief features created by volcanic activity: trenches, canyons, seamounts and ocean ridges. These are veritable oases in the depths where life abounds! Hydrothermal vents have been discovered here, consisting of black smokers expelling a very hot fluid (400 degrees) composed of chemical elements from the Earth’s interior (accretion zones) as well as cold sources (subduction zones). These ecosystems are sustained by different energy sources. They are hotbeds of biodiversity, providing essential habitats for many species that come to reproduce, feed or hide.
‘In 1977, the discovery of ecosystems associated with ocean ridges revolutionised our understanding of life on Earth!’ says Jozée Sarrazin. A profusion of animals live from hydrothermal vents near these underwater geysers, rich in sulphides and metals. ‘There, chemical energy is the driving force behind food webs. Thanks to microbial chemosynthesis, a whole endemic fauna thrives,’ explains the ecologist, who has been studying life in the deep sea for 30 years.
Crabs living near hydrothermal vents in the northeast Pacific. Photo taken during the Mescal Leg 1 2002 exploration campaign @IfremerThis biodiversity is as intriguing as it is fascinating. Who is there? What kind of environment does each species live in? How do they thrive in the darkness, under extreme pressure and temperature conditions? What are their restoration capabilities? What about their resilience? What role do they play in the overall functioning of the ocean?
The scientific community is conducting intensive observation, aided by technological advances.
All these discoveries, all this monitored data, all these samples collected and examined under a microscope hold promise for the human race.
A mineral paradise?
The seabed is teeming with life and coveted metals: iron, manganese, cobalt, nickel and copper. These components are widely used in electric cars, wind turbines and a whole range of digital devices.
The mining industry is targeting three types of mineral deposits. However, each is associated with specific ecosystems, some of which are islands of biodiversity that are home to endemic species that must be preserved.
Firstly, there are polymetallic nodules found in the Pacific, Atlantic and Indian oceans. Located on vast stretches of abyssal plains, these rock concretions are formed by the precipitation of minerals with seawater on an organic core. This is one of the slowest known geological processes, progressing at a rate of 2-10 mm/million years. It is therefore a non-renewable resource.
Next are rich deposits of sulphide minerals, formed around hydrothermal vents along ocean ridges (where tectonic plates meet) and certain underwater volcanoes. These were generated by hydrothermal fluid: this hot, corrosive water leaches the rocks of the oceanic crust and becomes loaded with metals and sulphides. When it gushes out from the sea floor, the metals precipitate on contact with the cold water and aggregate into large deposits at the ridges and oceanic arcs.
Polymetallic crusts form on the rocky flanks and walls of seamounts in thick layers several centimetres deep. They are rich in precious metals. Still little studied, the abundance, biodiversity and endemism of their fauna vary from site to site.
The full extent of these deposits is unknown, but the United States Geological Survey estimates, for example, that there are 21 billion tonnes of polymetallic nodules in the Clarion-Clipperton Zone (North Pacific).
Seabed mining © AFP Jonathan WALTER, Paz PIZARRO, Laurence SAUBADU
For scientists, the riches of the deep ocean are mainly biological resources (molecular, halieutic) currently being studied for our food, health, biomimicry, etc. ‘The physical and chemical conditions are unique in the depths, and the survival mechanisms developed by organisms can inspire us,’ says Pierre-Marie Sarradin, who heads the Beep laboratory. The chemist is particularly inspired by this study, which advocates sustainable use of the ocean based on knowledge, as opposed to use based solely on resources.
Scientific exploration: a vast field of study!
As a frontier of knowledge for the scientific community, a coveted space for its uses and a subject currently under discussion in international negotiations (within the AIFM but also in the context of the recent Treaty on the High Seas (BBNJ) and within the Climate and Biodiversity COPs), the deep ocean is a huge field of study!
Studying it also enables us to regulate it (through protection zones and bans or restrictions on deep-sea fishing). It also allows us to monitor seismic activity, characterise tectonics and assess and prevent underwater hazards. For example, an underwater volcano in Mayotte was discovered during a scientific expedition in May 2019, revealing intense geodynamic activity in the region.
Can we take the risk of destroying and causing irreversible damage before we know what we are dealing with? Today, research is organised around three objectives: understanding the dynamics of the deep ocean and how its ecosystems function; learning about and understanding the biogeochemical, geological and geophysical phenomena at work at the ocean-lithosphere interface; and observing the interactions between the deep ocean, the global ocean and the Earth system.
Demonstrate interdependencies, question connectivity
Everything is interconnected. The hydrothermal vent systems of ocean ridges illustrate these interdependencies. ‘This is where the interaction between the mantle and the outer layers of the Earth is at its strongest,’ explains Mathilde Cannat, a researcher at the Paris Institute of Earth Physics who is involved in the EMSO-Azores observatory.
Located on the Mid-Atlantic Ridge, the Lucky Strike hydrothermal field is a research site for understanding the ecosystem of the vents and how fauna and microorganisms adapt to this extreme environment. “They are subject to severe physical disturbances due to natural volcanic and tectonic activity. Despite this dynamic environment, our results show that these endemic biological communities are slowly recovering,‘ writes Jozée Sarrazin, who coordinates the European programme DeepRest. Between 2017 and 2024, her team observed the recovery capacity of the fauna in the hydrothermal vents: ’We conducted tests by creating disturbances,” explains the researcher. ‘We did not expect to see such a slow recovery to their initial state in seven years! ’.
In order to exploit the economically viable sulphide mineral deposits at certain hydrothermal sites, the mining industry claims that these sites are no longer active. The reason given is that abundant fauna tend to thrive in active sites. However, scientists have shown that the reality is more complex. The very notion of an ‘inactive site’ is debatable.
Mining risks drying up remaining springs or reactivating certain inactive deposits by altering hydrothermal circulation. ‘The reopening of old clogged conduits has already been demonstrated following the collection of fauna or rocks from apparently inactive deposits,’ writes Marie-Anne Cambon, a microbiologist and oceanographer, in The Conversation. Are these sites really inactive? Around the fast-spreading East Pacific Ridge, a study shows that microbial activity persists at inactive sites. ‘Even on the Atlantic Ridge, some sites thought to be inactive are in fact low-temperature sites M housing specific bacteria and fauna,’ warns the researcher.
Exploration of this area has been ongoing since 2014 with campaigns focusing on both geological (Hermine) and biological (Bicose) objectives, particularly as part of the Lifedeeper programme.
Understanding ecosystems to assess impacts
‘The exploitation of marine resources will have certain impacts on the environment. These will depend on the nature of the resource being exploited, the exploitation technology used and the specific characteristics of the associated ecosystems,’ warn Jozée Sarrazin, P-M Sarradin and François H. Lallier. In 2017, they described the anticipated impacts: destruction of habitats and associated fauna during ore collection, leading to the formation of a cloud of fine particles that could alter the turbidity and physico-chemical composition of the water column, sediment displacement, noise, vibrations and light.
They emphasised the importance of ecological connectivity: how would these disturbances affect the dispersal of fauna and larvae? They raised relevant questions that called for a better understanding of this biodiversity, including population dynamics, life cycles and genetic diversity.
Schematic representation of the environmental impacts of polymetallic nodule, polymetallic sulphide and cobalt-rich crust mining (from DYMENT et al., 2014)
In the Clarion-Clipperton abyssal plain, at the end of 2024, the Eden campaign continues to inventory new species. The aim is to better understand the links between biodiversity and polymetallic nodules. They are the only solid support available on the loose soils of the plains: a prime location for fixed organisms such as cold-water corals, sponges and cnidarians.
Around the nodules, crustaceans, echinoderms (including starfish), marine worms and microbial communities coexist. They are buried in the sediment and are extremely diverse. ‘The challenge is to catalogue them, but also to understand the role of each one in the ecosystem and their life cycles,’ explains Pierre-Antoine Dessandier, a researcher in benthic ecology. How is this diversity useful for the global ocean?
Researchers are also investigating the role of nodules in bottom currents and the deposition of organic matter. Do they provide a form of connectivity?
The team also sought to quantify the impacts of extraction: “After several years, we can still see traces of the collector’s caterpillars on the seabed. Our objective on site is to verify whether the fauna has been able to return and develop on the site since our visit. This is one of the great unknowns about species in the abyssal plains: what is their ability to recolonise an area disturbed by human activities?
A wide variety of species thrive on and around polymetallic nodules in the sediments of the abyssal plains of the Clarion-Clipperton Zone..@Ifremer
In July 2020, Japan conducted the first deep-sea test extraction of cobalt-rich crusts from the summit of Takuyo-Daigo Seamount in its exclusive economic zone (EEZ). Four scientists sought to assess the ecological impacts of extraction one month and thirteen months after the trial, both inside and outside the areas of induced sediment redeposition. Their studyshows that megafauna species (larger than 1 cm) abandon areas subject to the passage of excavating machinery, particularly the most mobile species.
Scientific questions are evolving as evidence of disruption emerges. The international community is warning of the real risks of biodiversity loss, which are very significant in areas targeted for mining. This is the case off the coast of Papua New Guinea, where a French team has described the high sensitivity of the fauna.
Environmental responsibility
The rules governing deep-sea mining ‘must be based on reliable scientific data’ and guided by ‘transparency and environmental responsibility,’ said Leticia Carvalho, secretary general of the AIFM, confirming a trend towards a pause (moratorium) last March.
‘Deep-sea mining poses major environmental, climate and economic risks, with highly uncertain benefits,’ said the International Coalition for the Protection of the Deep Sea.
‘Policy makers must therefore assess whether the economic pressures to extract minerals from the seabed are compatible with the protection of marine ecosystems and their biodiversity,’ says the European Academies’ Science Advisory Council (EASAC). To inform the ongoing debate in the European Union and beyond, it has published this document.
Value of knowledge
What sustainable solutions are emerging to slow down pressure and anticipate abuses? The Ethics Committee, composed of INRAE-Cirad-Ifremer-IRD, has highlighted the need to create a more robust legal status to protect the deep sea. The status of common heritage of humanity is not binding. The risk/benefit approach merely serves to develop a culture of impact.
In its opinion of June 2024, it refers to the status of ‘legal personality’, which would mean that the deep sea would no longer be considered an exploitable resource and its intrinsic and moral value would be recognised. This raises a fundamental question about the value of knowledge.
Isn’t it time for all stakeholders, from industry to research institutes and citizens, to mobilise around this supreme challenge?