Marine protection: Deep sea mining damages the seabed for a long time

Raw materials such as copper, cobalt and rare earth metals are scarce on land. Deep sea mining companies therefore want to mine them on the seabed. However, German researchers warn of the consequences: deep-sea mining affects the ecosystem of the seabed for a long time.

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  1. University of Konstanz, Konstanz
  2. State capital Stuttgart, Stuttgart

As part of of the Mining Impact project scientists are researching the effects and risks of underwater mining, especially the promotion of Manganese nodules. The project, which started in August 2018 and runs until February 2022, includes the Max Planck Institute for Marine Microbiology in Bremen, the Alfred Wegener Institute in Bremerhaven and the Geomar Helmholtz Center for Ocean Research in Kiel involved.

Researchers simulated degradation in the Pacific

The researchers have the ocean floor in the Discol area in the Pacific investigated, about 3,000 kilometers off the coast of Peru. There, in 1989, German scientists simulated the collection of manganese nodules from the sea floor by plowing the sea floor over an area of ‚Äč‚Äčabout three square kilometers with a harrow.

There are hardly any currents at a depth of 4,000 meters, which is why the traces of the experiment are still visible. "Even 26 years after this disruption, we could clearly see the plow marks on the sea floor", said Tobias Vonnahm from the Max Planck Institute for Marine Microbiology. Even small traces were still visible.

After 26 years, the traces of the harrow are still visible on the sea floor. (Image: ROV team / Geomar)

The changes on the seabed also have an impact on marine life: "The bacterial residents were significantly affected"said Vonnahme. About a third fewer bacteria lived in the old traces than in untouched seabed, in fresh plow traces it was even half less. The researchers found that the microbial processes were reduced by three quarters.

After all, the biogeochemical conditions have also changed sustainably, said project manager Antje Boetius. The main reason for this could be that the top, active sediment layer is destroyed or whirled up and carried away by the plow. The organic material that settles can only be used to a limited extent by the microorganisms and lose one of its key functions for the ecosystem. Accordingly, the microbes could act as indicators of damage to deep-sea ecosystems due to tuber degradation.

The raw materials lie on the ocean floor

The tubers, the size of potatoes to heads of lettuce, lie on the seabed. They mainly consist of iron and manganese, but also contain valuable metals such as cobalt, copper, nickel or titanium and to a very small extent rare earth metals, platinum metals or tungsten. These raw materials are important for the electronics industry, among others.

According to the researchers, all mining techniques that are currently being developed are disrupting the ocean floor to a depth of ten centimeters – as in the test in the Pacific. However, commercial mining would mean a disruption on a completely different scale: several hundred to several thousand square kilometers of seabed would be worked on each year.

Microbes need 50 years to recover

The resulting damage could have a lasting impact on the ecosystem: "Our calculations have shown that the microbes can only return to their normal function after 50 years at the earliest"said Vonnahme. The researchers present their results in an article in the journal Science Advances in front.

In addition to the manganese nodules, two other undersea raw material sources are being examined: over time, metals from the seawater are deposited on the slopes of mountains on the seabed. Form this cobalt-rich cruststo be scraped off. The third resource are Solid sulfides, metal-containing sulfur compounds, for example copper, zinc, gold, silver, indium, germanium, bismuth or selenium, which on undersea hydrothermal vents Black smokers, arise.

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