Interactive video: Deep sea mining
Companies are planning to extract minerals from areas of hydrothermal vents, deep on the seabed. The BBC's Science Editor David Shukman explains the process and environmental concerns.
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Deep sea vents
Hydrothermal vents are fissures on the seabed where water penetrates the Earth's crust and is heated to extreme temperatures by geological activity. The fluid which spurts from the vents is enriched with metals, minerals and dissolved gases. When this meets the surrounding cold seawater, it forms "black smoker" chimneys, some up to 20 metres high, emitting particle-rich plumes (pictured).
The deepest vents so far discovered lie almost 5,000 metres down in the Cayman Trough, an area of the Caribbean Sea. But other vent fields occur along the underwater mountainous ridges throughout the world's oceans. Despite the immense pressure and high temperatures, marine life has adapted to cope with the conditions in these extreme environments.
Sulphide compounds created by the interaction of seawater with molten rock build up in chimneys around the vents and continue to develop as further chemical reactions take place.
Among the most sought-after sulphides are the ores of gold, copper and zinc, used in electronics. Rare earth elements such as lanthanum and neodymium are also in high demand for their use in the strong magnets which help to power electrical motors. Although not as rare as their name suggests, these minerals are currently mined almost exclusively in China which can therefore dictate the world's supply.
One company, Nautilus, is working on a project to mine copper and gold from deep sea vents in an area off Papua New Guinea, at a depth of 1,600 metres. To do this, large robotic machines would excavate material by cutting into the rock. The cut material would be pumped as "seawater slurry" to a ship on the surface.
On board the ship, Nautilus say the slurry mixture would be "dewatered", shifting the solid material into a barge, while the used seawater would be pumped back down to the sea floor using pipes. Other companies, including a British firm, owned by US defence giant Lockheed Martin, are looking at another approach, "vacuuming" up small pieces of rock called nodules which lie on the seabed.
Specialist organisms have adapted to cope with extreme conditions at the vents, where life depends on chemosynthesis: conversion of chemicals to energy, rather than photosynthesis. Long tubeworms (right) rely on chemosynthetic bacteria for their nutrition which allows them to make use of the compounds emerging from the sea floor.
In recent years, scientists have discovered new species living near the deepest vents, including a shrimp which they have named Rimicaris hybisae (centre). It is eyeless but has a light sensitive panel on its back which may help it navigate by the glow around the vents. Anemones, clams and sea stars (left) have also been found thriving in the depths.