Leyland Cecco, The Guardian

Video footage from a deep-sea mining test, showing sediment discharging into the ocean, has raised fresh questions about the largely untested nature of the industry, and the possible harms it could do to ecosystems as companies push to begin full-scale exploration of the ocean floor as early as this year.

The Metals Company (TMC), a Canadian mining firm that is one of the leading industry players, spent September to November of last year testing its underwater extraction vehicle in the Clarion Clipperton Fracture Zone, a section of the Pacific Ocean between Mexico and Hawaii.

But a group of scientists hired by the company to monitor its operations, concerned by what they saw, posted a video of what they said was a flawed process that accidentally released sediment into the ocean. The scientists also said the company fell short in its environmental monitoring strategy, according to documents viewed by the Guardian.

In a post to its website, TMC acknowledged the incident, but framed the discharge from its cyclone separator as a “minor event” in which “a small amount” of sediment and nodule fragments spilled into the ocean. The company said it fixed the issue in its equipment to prevent further overflows and concluded that the incident “did not have the potential to cause serious harm”.

In a statement to the Guardian, the International Seabed Authority (ISA), a UN-affiliated agency set up to control and regulate deep-sea mining, said its preliminary assessment “identified no threat of harm to the environment” but it was waiting for a more detailed report of the incident from the company.

While many of the technologies used in deep-sea mining were developed decades ago, the inadvertent discharge during testing highlights the challenges of fine-tuning equipment for use in the field.

Experts and critics caution that the incident highlights the relative uncertainties surrounding deep-sea mining. Companies are scrambling to scavenge the ocean floor for valuable metals, used in electric vehicle batteries and a host of other technologies such as green energy production, amid a global fight for stable supply.

“What we’ve seen is an unauthorised release and, in terrestrial mining, this would have consequences of some sort. And the company says they told the regulator as a courtesy? This is bizarre,” said Catherine Coumans of MiningWatch Canada, adding that the incident runs counter to the assurances from companies that sediment won’t be released near the surface of the ocean.

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Critics have long feared the plumes of sediment created from extraction could seriously harm marine ecosystems by limiting light penetration and releasing harmful toxins. “We don’t know what the consequences of those problems were under the surface of the sea,” said Coumans. “We’re only seeing the tip of the iceberg. We’re not getting transparency.”

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