Biodiversity is depleted and large furrows still lie in the seabed where deep-sea mining equipment operated more than 40 years ago, in findings that suggest it will take the deep sea multiple decades to fully recover from mining activities.
Deep-sea nodules are packed with valuable metallic resources such as cobalt and manganese, critical components in electric car batteries and other devices.
In 1979, Ocean Minerals Company, a US firm, carried out test runs for nodule mining in an area of the Pacific Ocean known as the Clarion-Clipperton Zone. It was one of the first trials to carry out realistic nodule mining on the seabed, deploying a similar approach to plans set out by modern mining firms.
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鈥淭his is one of the oldest disturbance events that鈥檚 happened in the Clarion-Clipperton Zone,鈥� at the UK鈥檚 National Oceanography Centre told reporters in a briefing this week. 鈥淭his was very much the early days, to see if it was technologically feasible to harvest these nodules. And they proved that it was.鈥�
, Jones and his colleagues found that deep tracks remained in the seabed where the machines had trawled decades before.
The team used autonomous vehicles to assess biodiversity at the site. Some marine life had returned to the area, including single-celled organisms and larger animals such as sea cucumbers, but, overall, the site was still recovering, according to preliminary findings the team hasn鈥檛 yet published.
Biodiversity was still lower in the ploughed area compared with nearby, undisturbed regions of seabed. 鈥淲e started to see the first evidence of biological recovery,鈥� Jones said. 鈥淲e have not seen communities that are very much back to their normal status.鈥�
The findings support earlier research suggesting that ecosystems in mined areas suffer lasting change. In 2020, researchers found that microbial diversity in a region of the east Pacific used for mining tests in 1989 with analysis suggesting that mined regions would need at least 50 years for microbial activity to fully recover.
But some mining impacts do appear to have dissipated at the 1979 site. Based on model results, the team thinks the seabed surrounding the tracks would have been covered by a sediment plume in the immediate aftermath of the mining activity. Yet the sediment was no longer visible in 2023, Jones reported. 鈥淭he impact of the plume after 44 years seems relatively limited, which is quite encouraging for the overall impact of these mining effects,鈥� said Jones.
The mining equipment used in 1979 was about 9 metres wide, with a 2-metre propeller used on the seafloor. Modern machines are likely to be around twice that size and therefore should create more disturbance on the seafloor, Jones said.
