Simulated Deep-Sea Mining Reveals Damage to Seafloor Ecosystems

Researchers found tracks from the 1989 simulation still clearly visible on the seafloor, 13,000 feet beneath the surface.

(A) DEA plough track (photo by ROV Kiel 6000 Team, GEOMAR), showing the different microhabitat samples; (B) EBS track (photo by Ocean Floor Observation System, Alfred-Wegener Institute); and (C) the reference (photo by ROV Kiel 6000 Team, GEOMAR). (D to F) Schematic representation of the sampling design (A) and different microhabitats observed (figures by Autun Purser).

(CN) — German researchers have been looking at the smallest inhabitants of Earth’s seabeds to see how deep-sea ecosystems will be affected if large-scale mining takes place there.

The world’s deep-sea floor is covered in thousands of square miles of polymetallic nodules and crusts consisting mainly of manganese and iron. However, they also contain valuable metals such as nickel, cobalt, copper and some of the most important rare-earth metals used in the high-tech industry.

It’s predicted these resources could one day become scarce on land due to high demand for batteries, electromobility and digital technologies. Needless to say, these deep-sea marine deposits are very economically interesting.

Despite growing interest, there is currently no market-ready technology for deep-sea mining. Previous endeavors have resulted in a massive and lasting impact on the affected areas. Studies have shown that many sessile inhabitants of the seafloor depend on the nodules as a substrate and have yet to return to their ecosystem decades after a disturbance. Animals living in the seabed become substantially affected after disturbances as well.

In a study published Wednesday in the journal Science Advances, marine biologist Antje Boetius, group leader at the Max Planck Institute for Marine Microbiology and director at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, and her research team detail their travels to the site of the last known deep-sea disturbance to investigate conditions of the seafloor as well as the activity of its microorganisms. 

Known as the so-called DISCOL site, for DIS-turbance and re-COL-onization, this area sits in the tropical East Pacific, nearly 1,900 miles off the coast of Peru. In 1989, a team of German researchers simulated mining-related disturbances at the location by plowing the seabed in a manganese nodule area for about two miles, 13,000 feet under the ocean’s surface.

“Even 26 years after this disturbance, the plow tracks on the seabed were still clearly visible,” said first author Tobias Vonnahme, who participated in the study as part of his diploma thesis, in a statement accompanying the study. “And the bacterial inhabitants were also clearly affected.” 

Vonnahme and the team found that only about two thirds of the bacteria lived in the old tracks compared to the undisturbed regions of the seafloor, and only half in fresher plow tracks. The rates of various microbial processes were reduced by three quarters in comparison to undisturbed areas, even after a quarter of a century. 

“Our calculations have shown that it takes at least 50 years for the microbes to fully resume their normal function,” Vonnahme said.

Boetius stresses that although it is not surprising that even small-scale traces of the DISCOL experiment are still visible this far from the strong currents of the ocean’s surface, the biogeochemical conditions had undergone lasting changes. The researchers say this is because the plow destroyed the upper, active sediment layer, stirring it up and allowing it to be carried away by the currents. 

In the affected areas, the microbial inhabitants can only make limited use of the organic material that sinks to the seafloor from upper layers of the ocean so the disturbance results in the loss of one of their key functions for the ecosystem. Microbial communities then could be the proverbial canary in the coal mine— early indicators of damage to deep-sea ecosystems, as well as the extent of their potential recovery.

Technologies to mine the manganese nodules being currently developed will inevitably lead to a massive disturbance of the seabed down to a depth of at least four inches. The effects would be comparable to the disturbance simulated here, but on an entirely new scale as commercial deep-sea mining would affect hundreds to thousands of square miles of seabed per year and the plow tracks in the DISCOL combined only covered a few square miles. The authors predict that the expected damage will be correspondingly greater, and it would be correspondingly more difficult for the ecosystem to recover.

“So far, only few studies have dealt with the disturbance of the biogeochemical function of deep-sea floors caused by mining,” Boetius said. “With the present study, we are contributing to the development of environmental standards for deep-sea mining and pointing out the limits of seabed recovery. Ecologically sustainable technologies should definitely avoid removing the densely populated and bioactive surface layer of the seabed.”

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