Preliminary mining is expected to start in the new year, which the United Nations has coincidentally designated the International Year of the Ocean.
The plans envisage bringing about 10,000 tons to the surface in each of the first two years of operations, with volumes rising rapidly after that.
If this project is successful, other companies are expected to go into underwater mining. Already environmentalists are voicing concern.
Dr Sylvia Earle, one of the world's best known marine biologists, warns that "great care should be taken".
By another strange coincidence, the year - officially designated by the initiative of the United Nations Educational, Scientific and Cultural Organisation (Unesco) three years ago - is likely to witness a forceful reminder of the ocean's power over people at the same time, and in much the same area, as the mining opens a new dimension in human exploitation of the sea. The El Nino phenomenon - a warm Pacific current that disturbs weather all over the globe - which has been gathering pace this year, is expected to peak in the next 12 months. Scientists say it is likely to be one of the most severe this century, possibly the worst ever. The last big El Nino, in 1982-3, caused world-wide damage from drought, storms, floods, snow and fire which cost more than $8bn and killed at least 2,000 people.
This year's planned event - which will include more than 30 major conferences, a world-wide assessment of the state of the seas and the featuring of the ocean as the central theme of Expo '98 - is a belated recognition of the importance of 70 per cent of the world's surface.
It was not until we ventured into space and saw that our planet was mainly coloured blue that we realised it would be better titled Ocean than Earth. All the continents could be sunk into just one of the oceans, the Pacific, leaving plenty of space to spare. More than half the planet is under at least 9,000 feet of water.
Every living thing on land depends on the rain or snow brought on the wind from the seas. The oceans largely regulate the Earth's climate. But as Dr Frederico Mayor, the director general of Unesco, said in launching the year last week: "We probably know more about Mars than we do about the oceans."
Economists have calculated that the services provided by the world's seas - such as regulating the atmosphere, recycling nutrients and providing food and raw materials - are worth $21,000bn to humanity each year. In Asia alone, fisheries provide the livelihood for 200 million people as well as the main source of protein for a billion. Over 36 billion tons of oil and 21,000 billion tons of gas remain unexploited under the waters, and the waves and tides are likely to provide new sources of energy in the future.
Yet the world's oceans are increasingly under threat. Two thirds of the world's people live within 40 miles of the shores; within 30 years three- quarters will do so, a billion more people than are alive on the entire planet today.
The Food and Agriculture Organisation reports that every one of the world's major fisheries has reached or exceeded its limits; half are in serious decline. One of the greatest, the Grand Banks off Canada, has already been exhausted, throwing 35,000 fishermen out of work.
Half of the world's wetlands and mangrove swamps - ecosystems on which 90 per cent of the seas' fish depend - have already been destroyed. Unesco says that between five and 10 per cent of all coral reefs are being ruined each year. Intensive agriculture and the felling of forests inland send silt down the rivers doing further damage, while the building of dams upstream causes yet more disruption. Some three-quarters of the pollution of the seas comes from the land; much originates far away and is carried down the rivers or on the winds to the ocean.
The Black Sea is in severe danger and other largely enclosed seas, like the Baltic and the Mediterranean, are particularly vulnerable. Most of the pollution hugs the coast, where it poses the greatest hazard to people. There is also increasing evidence of contamination of the open oceans - much of it concentrated in a thin film on the surface of the water which is also where the larvae, eggs and micro-organisms that form the foundation of the life of the seas are concentrated.
Up to now, most international action has focused on relatively minor problems such as oil pollution from ships, or protecting whales.
Elizabeth Dowdeswell, the outgoing head of the United Nations Environment programme said: "We have been merely tinkering with the symptoms. Whether the world will do any better in the official International year of the Oceans remains to be seen."
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