The transition from a global hydrocarbon economy to a green energy economy and the rapidly growing middle class in developing countries are driving the need for considerable new sources of critical materials. Deep-ocean minerals, namely cobalt-rich ferromanganese crusts and polymetallic nodules, are two such new resources generating interest.

Polymetallic nodules are essentially two-dimensional mineral deposits sitting on abyssal plain sediments at about 3,500–6,000 m water depths. Metals of economic interest enriched in nodules include nickel, copper, manganese, cobalt and molybdenum. Cobalt-rich ferromanganese crusts are also two-dimensional deposits forming pavements on rock outcrops on seamounts and ridges at water depths of 400–7,000 m. Metals of economic interest for crusts include cobalt, manganese, nickel, molybdenum, tellurium, platinum, vanadium and rare earth elements.

A conservative estimate is that 21.1 billion dry tons of polymetallic nodules exist in the Clarion-Clipperton Zone (CCZ) manganese nodule field, the largest in area and tonnage of the known global nodule fields. Based on that estimate, tonnages of many critical metals in the CCZ nodules are greater than those found in global terrestrial reserves. About 7.5 billion dry tons of cobalt-rich ferromanganese crusts are estimated to occur in the Pacific Ocean Prime Crust Zone, the area with the highest tonnage of critical-metal-rich crust deposits, with many elements contained therein estimated to be greater than those found in global terrestrial reserves.

Deep-ocean mining has not yet been carried out in the Exclusive Economic Zone of any nation, nor in the Areas beyond national jurisdiction, although extensive mineral exploration and environmental studies are being conducted and exploitation regulations codified, indicating that mining activities will likely begin in the near future. If deep-ocean mining follows the evolution of offshore production of petroleum, we can expect that about 35–45 per cent of the demand for critical metals will come from deep-ocean mines by 2065.