Scientists Warn of Wide Impacts on Midwaters Around Deep-Sea Mining Sites

The mid-depths of the oceans contain a vast diversity of life. Squid, fish, shrimp, copepods, medusa, filter feeding jellies and marine worms are among the creatures that could be affected by deep-sea mining. (Photos © by E. Goetze, K. Peijnenburg, D. Perrine, Hawaii Seafood Council (B. Takenaka, J. Kaneko), S. Haddock, J. Drazen, B. Robison, DEEPEND (Danté Fenolio) and MBARI)

Interest in deep-sea mining for copper, cobalt, zinc, manganese and other valuable metals has grown substantially in the last decade, and mining is anticipated to begin soon in some areas. But a new study argues that deep-sea mining poses significant risks not only to the area immediately surrounding mining, but also to the water hundreds to thousands of feet above the seafloor, threatening vast mid-water ecosystems. The scientists suggest how these risks could be evaluated more comprehensively to enable society to decide if and how deep-sea mining should proceed. The paper, published this week in the Proceedings of the National Academy of Sciences, provides a first look at potential threats to the midwater, or pelagic, system.

The deep mid-waters of the world’s ocean represent more than 90 percent of the biosphere, contain 100 times more fish than the annual global catch, connect surface and seafloor ecosystems, and play key roles in climate regulation and nutrient cycles.

Currently, 30 exploration licenses cover about 580,000 square miles of the seafloor on the high seas, and some countries are exploring exploitation in their own waters. Most research assessing the impacts of mining and environmental baseline survey work has focused on the seafloor.

Though largely unexplored, the oceans’ mid-depth waters harbor a rich biomass that is tightly intertwined with humanity. Large amounts of mud and dissolved chemicals would be released during mining, and large equipment produces extraordinary noise—all of which could travel vertically and horizontally for long distances. But there has been almost no study of the potential effects of mining beyond the habitat immediately adjacent to extraction activities.

“The study shows that mining and its environmental impacts may not be confined to the seafloor thousands of feet below the surface, but could threaten the waters above the seafloor, too,” said paper coauthor Pierre Dutrieux, an oceanographer at Columbia University’s Lamont-Doherty Earth Observatory. “Harm to midwater ecosystems could affect fisheries, release metals into food webs that could then enter our seafood supply, alter carbon sequestration to the deep ocean, and reduce biodiversity.”

“Mining is poised to move forward, yet we lack scientific evidence to understand and manage the impacts on deep pelagic ecosystems. More research is needed very quickly,” said Jeffrey Drazen, lead author of the article and professor of oceanography at the University of Hawaii, Manoa.

In accordance with UN Convention on the Law of the Sea, the International Seabed Authority is required to ensure the effective protection of the marine environment, including deep midwater ecosystems, from harmful effects arising from mining-related activities. In order to minimize environmental harm, mining impacts on the midwater column must be considered in research plans and development of regulations before mining begins.

“We are urging researchers and governing bodies to expand midwater research efforts, and adopt precautionary management measures now in order to avoid harm to deep midwater ecosystems from seabed mining,” said Drazen.

Funding for this work was provided by the Schmidt Ocean Institute and the Gordon and Betty Moore Foundation.

Earth Institute. Adapted from a press release by the University of Hawaii, Manoa.

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