Deep-sea mining dust clouds travel long distances, researcher finds

New research has found that even though the ‘dust clouds’ created by deep-sea mining descend at a short distance for the most part, a small portion of the stirred-up bottom material remains visible in the water at long distances.

“These waters are normally crystal clear, so deep-sea mining could indeed have a major impact on deep-sea life,” marine geologist Sabine Haalboom, who studied this phenomenon for her PhD dissertation at Utrecht University in the Netherlands, said in a statement.

Haalboom pointed out that deep-sea mining may take place at depths whose underwater life is yet to be described.

The silt at the bottom of the deep sea which would be stirred up when extracting mineral-rich manganese nodules most deep-sea miners are after. Since life in the deep sea is largely still unknown, it’s unclear what effects clouding the water could have.

For her research, Haalboom conducted experiments with different instruments to measure the amount and also the size of suspended particles in the water. At the bottom of the Clarion-Clipperton Zone, a vast area in the depths of the Pacific Ocean, she performed measurements with those instruments before and after a grid with 500 kg of steel chains had been dragged across the bottom.

“The first thing that strikes you when you take measurements in that area is how unimaginably clear the water naturally is,” the scientist noted. “After we dragged the chains back and forth over a 500-metre stretch, the vast majority of the stirred-up material settled within just a few hundred metres. Yet, we also saw that a small portion of the stirred-up bottom material was still visible up to hundreds of metres from the test site and metres above the bottom. The water was a lot murkier than normal at long distances from the test site.”

In a follow-up study, in which Haalboom was not involved, the “dust clouds” were visible even up to 5 km away from the test site.

Companies competing for concessions to extract metals from the deep-sea floor are seizing on the results of these initial trials as an indication of the low impact of deep-sea mining on bottom life. Yet, that is not justifiable, said Henko de Stigter, co-promoter of Haalboom’s research and an oceanographer at the Royal Netherlands Institute for Sea Research.

“Sure, based on this PhD research and also based on follow-up research, we know that the vast majority of the dust settles quickly. But when you take into consideration how clear these waters normally are, and that deep-sea life depends on the very scarce food in the water, that last little bit could have a big impact,” he said.

Both Haalboom and De Stigter urge more research before firm statements can be made about the impact of deep-sea mining.

“It is really too soon to say at this point how harmful or how harmless that last bit of dust is that can be spread over such great distances,” de Stigter emphasized.