Battle Over Deep-Sea Mining Takes on New Urgency as Trial Run Winds Down

“The seafloor plume is hugging the seafloor,” he said.

Still, the company’s own consultants acknowledged it was too early to draw any conclusions.

“There is really a lot of data to analyze before you can make an assessment of environmental impacts,” Thomas L. Johnson of DHI Group, hired by the Metals Company to study the sediment plume, said in a telephone interview from the expedition site.

The test mission has experienced some mishaps, including electrical wiring failures related to deep-sea pressures and the dumping of rock fragments and sediment-laden wastewater from the ship, according to documentation reviewed by The New York Times. A spokesman for the Metals Company said the discharge resulted from a surge in water flowing through a sediment-scrubbing device and “was not deemed to be a significant hazard or risk to the environment.” The test is scheduled to conclude by the middle of this month.

Matthew Gianni, a co-founder of the Deep Sea Conservation Coalition, said small amounts of dispersed sediment and the simple removal of the rocks — which are a habitat for many seabed organisms — may be enough to disrupt life.

“If you don’t even know species that are out there and how they react to this sediment, then you can’t make any assertion of what the biological impact of plumes will be,” he said. “Put the evidence on the table. Submit it to independent scientists to scrutinize and see if their assertions hold up. Until then, we cannot even talk about moving ahead on large-scale mining.”

A spokeswoman for the International Seabed Authority did not respond to questions about the test. The agency, with a staff of about 50, did not send a full-time employee on the expedition, and instead sent a trainee, a Metals Company official said.

The test is taking place about 1,100 miles southwest of Manzanillo, Mexico, using remotely operated vehicles because the water is so deep and the pressure so intense it is generally too complicated to send workers. Marine historians say it is probably the largest ever collection of seabed nodules from the minerals-rich area, which is known as the Clarion-Clipperton Zone.