Few people have seen the polymetallic nodules scattered across the ocean floor 4 kilometres down. Rob McCallum, a divemaster and founder of EYOS Expeditions, has descended into the Clarion-Clipperton Zone in the Pacific, a vast area earmarked for deep-sea mining. He describes the nodules, which contain nickel, cobalt, copper and manganese used in batteries, as "anywhere between the size of a potato or a baseball, and they are black."
McCallum, who has explored all five oceans and visited the wrecks of the Titanic and the Bismarck, likens the nodules to nuggets from Australia's gold rush era. But he is wary of the industry's promises. "I'm always worried when the message sounds too good to be true and, when you start poking holes, people get defensive," he said.
Billions have already been invested in exploration as governments and companies position themselves to tap a new source of critical minerals. United States President Donald Trump signed an executive order last year to accelerate seabed mining in US and international waters, arguing it would secure supplies and reduce dependence on China. In August, the US announced plans to sell deep-sea mining leases in waters around the Marianas and American Samoa.
Mining companies have forecast billions in potential profits, with royalties flowing to Pacific nations that open their waters to the industry. But McCallum and other undersea experts question the viability of the venture, fearing the only winners will be early investors and the companies selling the machinery needed to mine the ocean floor.
Commercial deep-sea mining is not yet legal. The International Seabed Authority (ISA) is finalising a framework to govern environmental, financial and regulatory requirements, under which companies would need to demonstrate the technical and financial capacity to carry out mining operations. The technical hurdles are significant, including operating under extreme pressure thousands of metres below the surface.