New research shows how seabed mining disrupts the food web

As the US moves to license deep sea mining, new research finds extracting critical metals from the seabed generates waste that endangers tiny marine organisms which form the basis of a vast food web. The impacts have the potential to disrupt commercial fisheries and what lands on dinner plates.

In the first-of-its-kind study published on Nov 6 in Nature Communications, scientists analysed data from a 2022 test mining operation conducted by The Metals Company (TMC) in the Pacific Ocean. TMC in April applied for a licence from the Trump administration to mine the same area of the ocean, which is controlled by a UN-affiliated organisation. 

During the mining trial, a robot collected metal-rich rocks from the seabed at a depth of 4,000m. The avocado-sized rocks, called polymetallic nodules, were transported to a surface ship where they were separated from water, sediment and mineral fragments. The plume of wastewater was then pumped back into the ocean at a depth of 1,250m. 

Known as the “twilight zone”, that part of the ocean is home to zooplankton and other small organisms that provide nutrition for the entire food chain, including top predators and species that humans fish for, like bluefin tuna, mahi-mahi and swordfish. 

Zooplankton feed on microscopic particles in the water column. When the researchers collected samples of nodule and sediment debris and compared them to particles zooplankton eat, they found mining particles were similar in size but far more numerous and nutritionally poorer.  They determined the abundance of mining particles would “drastically dilute” the nourishment zooplankton need to survive. 

A full-scale mining operation would likely have “a significant impact to the nutritional input for this community, and this could lead to a reduction in commercial fisheries catch that would affect us”, said Mr Michael Dowd, lead author of the peer-reviewed paper and a doctoral student at the University of Hawaii at Manoa.

Zooplankton also play a crucial role in the biological pump, a process that transports carbon dioxide from the surface and sequesters it in the deep ocean, the researchers noted.

Despite the possibility that deep sea mining operations could begin within the next few years, mining waste’s impact on the twilight zone has been little studied, and no international standards have been set for what depth nodule debris should be discharged. 

TMC, which cooperated in the study and shared data with the researchers, has stated in regulatory filings that it would dispose of mining waste at a depth of 2,000m during commercial operations.

 “The sediment dilutes to background concentrations very rapidly on release as it disperses into the vastness of the Pacific,” Dr Michael Clarke, TMC’s environmental manager, said in an e-mail.

“Concern about midwater impacts is understandable, but the data have moved on – and so should the conversation,” he added.

The researchers said that such depths are among the most poorly studied regions of the ocean, and it remains unknown to what extent mining waste discharged at 2,000m could affect the food web higher up the water column.

Associate Professor Erica Goetze, a co-author of the paper and a zooplankton expert at the University of Hawaii, said the organisms are also found at that depth.

“Moving the discharge plume deeper in the water column will move it into a region with lower overall absolute abundances of animals. But the communities that reside there will suffer similar impacts,” she said in an e-mail. BLOOMBERG