It Could Take Decades For The Ocean Floor To Recover From Deep Sea Mining

It Could Take Decades For The Ocean Floor To Recover From Deep Sea Mining
A sponge attached to a polymetallic nodule (Photo: GEOMAR, ROV Kiel 6000)

A new study has found that the impacts of deep sea mining are still felt a quarter of a century later.

As the need for metals like copper, nickel, and cobalt mount, some have looked to harvest them from a vast field of metal-rich rocks called polymetallic nodules in the Pacific. Yet there haven’t been many experiments studying its impact on the seafloor ecosystems. A new paper published on Wednesday in Science Advances looks a study site off of the coast of Peru and reveals long-term impacts to the base of the food chain in seafloor communities.

Back in 1989, scientists undertook the disturbance and recolonization experiment, or DISCOL, to assess the impacts of deep sea mining for polymetallic nodules. Researchers plowed and disturbed the sediment of a nearly 10-metre wide area of the seafloor abour 14 kilometres beneath the ocean’s surface and have observed the changes to the area since.

Now, researchers led by Tobias Vonnahme at the Max-Planck Institute for Marine Microbiology in Germany have come back to compare the microbial activity in the DISCOL plow tracks compared to both more recently disturbed areas and unplowed seafloor, using images and samples taken from both a remotely operated and an autonomous underwater vehicle.

Even after 26 years, the DISCOL plow tracks were still apparent in images taken by the underwater vehicles. The researchers also observed decreased biological activity in both the fresh tracks and the 26 year old tracks. The total number of microbes was cut in half by ploughing fresh tracks while they were still 30 per cent lower in the DISCOL tracks. The researchers estimated that microbial activity in plowed tracks would take 50 years to recover.

Sampling the DISCOL plow tracks (Photo: GEOMAR, ROV Kiel 6000)

While it’s a positive sign that some recovery happened, the study foretells trouble when put into context with other work. Last year, scientists analysing the DISCOL site found fewer suspension feeders—animals that feed on organisms suspended in the water—and overall less animal diversity in the plowed areas. That study published in Nature concluded that “the impacts of polymetallic nodule mining there may be greater than expected, and could potentially lead to an irreversible loss of some ecosystem functions, especially in directly disturbed areas.”

The impacts on seafloor microbes are particularly notable. They’re essentially the first level of the food web for sea floor communities. Researchers not involved in the study agreed with the newest work’s importance.

“If deep-seabed mining moves forward, it will be on spatial and temporal scales that are orders of magnitude greater than this experiment,” Diva Amon, deep-sea biologist and scientific associate at the Natural History Museum in the United Kingdom told Earther in an email. That means that recovery will take even longer.

Amon’s own work found that over 50 per cent of large seafloor-dwelling species rely on these nodules in order to anchor themselves, so “given that nodules take millions of years to form, the expected prognosis for recovery of this community is very low.”

A polymetallic nodule (Photo: Manfred Schulz TV & Film; Max Planck Institute for Marine Microbiology)

Daniel Jones, associate head of the Ocean Biogeosciences and Ecosystems Group at the National Oceanography Centre in the United Kingdom, agreed that the study was extensive and carried out by a world-class team. But he cautioned in an email that the DISCOL study area differs from the Clarion-Clipperton Zone (CCZ) where there’s the most interest in deep-sea mining—the CCZ has less food supply than the Peru Basin.

“It would be very valuable to see how the findings at DISCOL compare to those in areas likely to be directly impacted by mining,” he told Earther in an email. “Hopefully we won’t have to wait too long, a range of new projects are already planning to address this challenge in the CCZ.”

Data is mounting that deep-sea mining can have negative, and potentially irreversible impacts on the delicate ecosystems at the bottom of the ocean. The International Seabed authority is in the midst of putting together regulations on how to mine the seafloor, after which extraction is due to begin. But scientists are worried that mining might start before we really know what the impact of the mining will be, according to Nature. And studies are showing that the impact will not be good.