Continental plates The Earth’s crust is made up of numerous continental plates that are in permanent motion. They move a few centimetres each year. This continental drift means that plates are veering away from each other in some places. At these plate boundaries the Earth’s crust is splitting apart. Fresh magma is continuously being extruded from the fissures and, over time, it piles up on the ocean floor to form large undersea ridges.
The sea floor – humankind’s resource repositoryThe oceans hold a veritable treasure trove of valuable resources. Sand and gravel, oil and gas have been extracted from the sea for many years. In addition, minerals transported by erosion from the continents to the coastal areas are mined from the shallow shelf and beach areas. These include diamonds off the coasts of South Africa and Namibia as well as deposits of tin, titanium and gold along the shores of Africa, Asia and South America. Efforts to expand ocean mining into deep-sea waters have recently begun. The major focus is on manganese nodules, which are usually located at depths below 4000 metres, gas hydrates (located between 350 and 5000 metres), and cobalt crusts along the flanks of undersea mountain ranges (between 1000 and 3000 metres), as well as massive sulphides and the sulphide muds that form in areas of volcanic activity near the plate boundaries, at depths of 500 to 4000 metres.
- Back in the early 1980s there was great commercial interest in manganese nodules and cobalt crusts. This initial euphoria over marine mining led to the International Seabed Authority (ISA) being established in Jamaica, and the United Nations Convention on the Law of the Sea (UNCLOS) being signed in 1982 – the “constitution for the seas”. Since entering into force in 1994, this major convention has formed the basis for signatories’ legal rights to use the marine resources on the sea floor outside national territorial waters (Chapter 10).
- After that, however, the industrial countries lost interest in resources. For one thing, prices dropped – making it no longer profitable to retrieve the accretions from the deep sea and utilize the metals they contained. Also, new onshore deposits were discovered, which were cheaper to exploit. The present resurgence of interest is due to the sharp increase in resource prices and attendant rise in profitability of the exploration business, and in particular to strong economic growth in countries like China and India which purchase large quantities of metal on world markets. Even the latest economic crisis is not expected to slow this trend for long. The industrial and emerging countries’ geopolitical interests in safeguarding their supplies of resources also play a role. In light of the increasing demand for resources, those countries which have no reserves of their own are seeking to assert extraterritorial claims in the oceans.
Manganese nodulesCovering huge areas of the deep sea with masses of up to 75 kilograms per square metre, manganese nodules are lumps of minerals ranging in size from a potato to a head of lettuce. They are composed mainly of manganese, iron, silicates and hydroxides, and they grow around a crystalline nucleus at a rate of only about one to 3 millimetres per million years. The chemical elements are precipitated from seawater or originate in the pore waters of the underlying sediments. The greatest densities of nodules occur off the west coast of Mexico (in the Clarion-Clipperton Zone), in the Peru Basin, and the Indian Ocean. In the Clarion-Clipperton Zone the manganese nodules lie on the deep-sea sediments covering an area of at least 9 million square kilometres – an area the size of Europe. Their concentration in this area can probably be attributed to an increased input of manganese-rich minerals through the sediments released from the interior of the Earth at the East Pacific Rise by hydrothermal activity – that is, released from within the Earth by warm-water seeps on the sea floor and distributed over a large area by deep ocean currents.
- 7.4 > The sea floor contains extensive resources. They are concentrated in certain regions depending on how they were formed.
- Cross-section view of a manganese nodule: Over millions of years, minerals are deposited around a nucleus.
- Manganese nodules are composed primarily of manganese and iron. The elements of economic interest, including cobalt, copper and nickel, are present in lower concentrations and make up a total of around 3.0 per cent by weight. In addition there are traces of other significant elements such as platinum or tellurium that are important in industry for various high-tech products. The actual mining process does not present any major technological problems because the nodules can be collected fairly easily from the surface of the sea floor. Excavation tests as early as 1978 were successful in transporting manganese nodules up to the sea surface. But before large-scale mining of the nodules can be carried out there are still questions that need to be answered. For one, neither the density of nodule occurrence nor the variability of the metal content is accurately known. In addition, recent investigations show that the deep seabed is not as flat as it was thought to be 30 years ago. The presence of numerous volcanic elevations limits the size of the areas that can be mined. Furthermore, the excavation of manganese nodules would considerably disturb parts of the seabed. The projected impact would affect about 120 square kilometres of ocean floor per year, an area the size of the city of Kiel. Huge amounts of sediment, water, and countless organisms would be dug up with the nodules, and the destruction of the deep-sea habitat would be substantial. It is not yet known how, or even whether, repopulation of the excavated areas would occur. Since 2001 several permits have been issued to governmental institutions by the ISA to survey manganese fields. These are not for actual mining but for a detailed initial investigation of the potential mining areas. In 2006 Germany also secured the rights to a 150,000 square kilometre area – twice the size of Bavaria – for a period of 15 years. Last year, for the first time, industrial companies also submitted applications for the exploration of manganese nodule fields in the open sea in cooperation with developing countries (Kingdom of Tonga, Republic of Nauru). >