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In 1972, a young ecologist named Hjalmar Thiel ventured to a remote part of the Pacific Ocean known as the Clarion–Clipperton Zone (CCZ). The sea floor there boasts one of the world’s largest untapped collections of rare-earth elements. Some 4,000 metres below the ocean surface, the abyssal ooze of the CCZ holds trillions of polymetallic nodules — potato-sized deposits loaded with copper, nickel, manganese and other precious ores.

Thiel was interested in the region’s largely unstudied meiofauna — the tiny animals that live on and between the nodules. His travel companions — prospective miners — were more eager to harvest its riches. “We had a lot of fights,” he says. On another voyage, Thiel visited the Red Sea with would-be miners who were keen to extract potentially valuable ores from the region’s metal-rich muds. At one point, he cautioned them that if they went ahead with their plans and dumped their waste sediment at the sea surface, it could suffocate small swimmers such as plankton. “They were nearly ready to drown me,” Thiel recalls of his companions.

In a later confrontation, Thiel — who was at the University of Hamburg in Germany — questioned how industry planned to test the environmental impacts of sea-bed mining. He was curtly advised to do his own test. So he did, in 1989.

Thirty years on, the test that Thiel and a colleague devised is still the largest experiment ever on the potential impacts of commercial deep-sea mining. Called DISCOL, the simple trial involved raking the centre of a roughly 11-square-kilometre plot in the Pacific Ocean with an 8-metre-wide implement called a plough harrow. The simulated mining created a plume of disturbed sediment that rained down and buried most of the study area, smothering creatures on the sea floor. The test revealed that the impacts of sea-bed mining reached further than anyone had imagined, but it did not actually extract any rocks from the sea bed, which itself would have destroyed even more marine life.

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Category: Science