Deep seabed mining in 5 questions

. COP27, Egypt. Emmanuel Macron declares, before an assembly of heads of state and governments from all over the world, that France supports the prohibition of all mining of the deep seabed. If the country - the first maritime area in the world - is taking a big step forward, the game is not however won to protect the deep sea. Why exploit them, what are these coveted minerals, where are they, what does the law say, what are the threats to the environment? Answers in our article.

What is deep seabed mining?

The exploitation of the seabed, also called deep sea mining, consists in extracting rare metals and materials present in the depths of the ocean (200 meters below sea level) in order to satisfy our technological need and ensure, paradoxically, the energy transition: manufacture of electronic devices (such a batteries and mobile phones), construction of wind turbines, photovoltaic panels and more.

A report from the French Senate dated June 21, 2022 specifies that there are about forty years left for copper, cobalt and nickel before the depletion of stocks on continental surfaces.

"From a technological point of view, the industrialists are already ready: ready to bring down large machines to mow the deep corals, scrape the sulfide mountains, harvest the nodules from the abyssal plains and bring it all up via a large pipe to a boat that will treat, sort and discharge useless sludge into the ocean", deplores François Lallier, professor at Sorbonne University assigned to the Roscoff Biological Station and member of the ministerial steering committee for the objective "Deep seabed" of France 2030.

Which minerals are coveted by industrialists?

There are three of them:
  • Polymetallic nodules. These "big potatoes" rest on the ocean floor between 4,000 and 6,000 meters deep. They contain a wide variety of metals such as iron, manganese, cobalt, copper, nickel or lead. "Nodules take hundreds of millions of years to form. If the industrialists harvest them, they will not grow back for ages! Admittedly, it is a resource, but it is non-renewable", specifies François Lallier.
  • Cobaltiferous crusts. These are plates about ten centimeters thick that are found on the walls of seamounts. They are rich in iron, manganese and cobalt. The crusts also contain high concentrations of precious metals (platinum) and rare metals.
  •  Polymetallic sulfides. They are found in hydrothermal vents near ocean ridges and submarine volcanoes, between 1,000 and 5,000 meters deep. Sulfides are particularly promising because they contain a large number of base metals (copper, zinc, lead) and precious metals (gold, silver).


Where are they found?

These mineral resources are present in all the oceans of the globe, but more particularly, in the central basin of the Indian Ocean, around the Cook Islands, Kiribati and French Polynesia, in the seamounts of Magellan, in the Pacific Ocean, east of Japan.

On Earth, we can replant trees after a deforestation. But at the bottom of the ocean, how do we do it?
François Lallier, professor at Sorbonne University

What does the law say?

There are two legal frameworks for the deep seabed:  
  • The territorial waters and the exclusive economic zone (EEZ) of each State, up to two hundred nautical miles. "Each State is free to authorize or prohibit fishing such as deep-sea exploitation in an EEZ. It is under national jurisdiction", underlines François Lallier. In the world, France is the territory which has the largest exclusive zone (11,691,000 million km²) ahead of the United States, with a high proportion of deep seas around the overseas departments and territories: Antilles, Reunion, Polynesia and New Caledonia.
  • International waters, also called the "Zone". The seabed outside territorial waters and EEZs belongs to the common heritage of humanity. This was decided by the United Nations Convention on the Law of the Sea (Montego Bay Convention) in December 1982. Twelve years later, the UN set up the International Seabed Authority (AIFM) which oversees, issues and distributes seabed exploration and exploitation permits (outside EEZs) between countries. Recently, the AIFM issued a "test" seabed mining permit to the Canadian company, The Metals Company, whose long-term objective is to harvest 1.3 million tons of ore per year.

What would be the consequences for the planet?

  • The impact of extraction plumes in the deep sea: while digging to collect metals, extraction machines would move particles and create typical plumes that "could remain in suspension much longer than on Earth," says François Lallier. When hydrothermal vents were discovered, it was noticed that many animals congregate on these natural vents. Complex ecosystems composed of organisms adapted to this particular environment have developed there. The toxic elements expelled by these plumes could then impact abyssal organisms that are not adapted to these extreme conditions.
  • The impact on marine mammals: we are talking here about light pollution caused by the presence of operating vessels, but also sound pollution-very low frequency sounds could interfere with those of marine mammals and the increase in maritime traffic would increase ambient noise, generating vibrations in ocean areas previously devoid of human activity.

  • The impact on deep-sea fauna: deep-sea species generally have a longer life span, a later sexual maturity and a slower growth rate in the deep sea. This could lead to a decrease in the reproduction of these animals, or even extinction.
    "On the tops of seamounts, there is a lot of fauna, including deep-sea corals and associated species. There are also many fish. It’s very lively! But the growth is slow on these mounts, it would take at least a hundred years for the fixed fauna to grow back for example. We must also mention the aspect of recolonization after exploitation: on Earth, we can replant trees after a deforestation. But on the ocean floor, how do you do that?" says François Lallier.

  • The impact on carbon sequestration: 30% of CO2 is absorbed by the ocean and stored in the seabed. Mining could lead to the release of carbon stored in the depths.