Mineral resources of the World Ocean as a source of plant nutrients

For an agronomist, the World Ocean is primarily of interest as a colossal source of plant nutrients. Magnesium, sulfur, calcium, potassium, boron, copper, and zinc are contained in seawater and bottom sediments in gigantic quantities. However, the accessibility of these resources for the production of mineral fertilizers depends directly on economic feasibility and the technologies for their extraction.

Seawater resources and shelf potential

Oceans cover 70.8% of the Earth's surface with an average depth of 3.96 km. This is a vast reservoir of dissolved substances washed out from land rocks and emitted by underwater volcanoes. The average salinity of water is 3.5%, with sodium, chlorine, magnesium, sulfur, calcium, and potassium accounting for 99.5% of all dissolved salts.

Every cubic kilometer of seawater holds dissolved reserves of another 64 elements. On average, one cubic kilometer contains 2000 kg of zinc and copper, 800 kg of tin, 280 kg of silver, and 11 kg of gold. The total reserves of dissolved gold are estimated at 10 billion tons, and uranium at about 4 billion tons. Today, it is profitable to extract only four resources from water: sodium and chlorine (as salt), magnesium, and bromine.

• Share of oceanic magnesium in global production — 61%
• Share of bromine extracted from water — 70%
• Share of table salt from seawater — 1/3
• Shelf area relative to the ocean surface — 7.5%
• Share of underwater coal in Japan's production — more than 20%

The shelf is a shallow terrace bordering continents where sedimentary rocks actively accumulate. Research and development of the mineral wealth of the shelf have been underway since the 60s of the last century. Oil, gas, magnetite and titanomagnetite sands, placer gold, platinum, as well as copper, tin, cobalt, diamonds, sulfur, and phosphorites are extracted here. In England, underwater coal mining provides 10% of the total national volume.

Deep-sea deposits and barriers to extraction

At great depths, the floor of the Pacific, Indian, and Atlantic oceans is covered with ferromanganese nodules. In the Pacific Ocean alone, their mass is estimated at 1500 billion tons, and the projected reserves of copper, nickel, and cobalt in them amount to 20–25 billion tons. These ore accumulations contain 20 times more cobalt, 90 times more nickel, and 42 times more manganese than all explored land deposits.

According to researchers' forecasts, the extraction of nodules on the ocean floor could cover global needs:

• for cobalt — by 50%;
• for manganese — by 18%.

Thanks to deep-sea nodules, global needs could be met for vast periods: for copper — for 3,000 years, nickel — for 70,000 years, manganese — for 140,000 years, cobalt — for 420,000 years. Deep zones also contain diatomaceous and globigerina oozes, rich in calcium and silica, and red clay, which consists of 25% aluminum oxide. In the rifts of the Red Sea off the coasts of Sudan and Saudi Arabia at depths of up to 2000 m, dozens of mud deposits rich in silver, zinc, and copper have been discovered.