Bringing awareness to oceanic midwaters: Implications of deep-sea mining

By Jessie Perelman, Safina Center Launchpad Fellow

In August 2018, I had the opportunity to help facilitate a scientific workshop at the University of Hawaiʻi at Mānoa to discuss a pressing, yet often overlooked, aspect of deep-sea mining: oceanic midwaters, the marine region that extends below the surface to just above the seafloor. The goal of this workshop was to compile and present a comprehensive analysis of midwater habitats in the context of deep-sea mining and relay this to both the public and mining stakeholders. So, almost two years after these initial discussions, we published an article in the Proceedings of the National Academy of Sciences last week week that explores the importance and intricacies of oceanic midwaters and how they could be impacted by deep-sea mining.

The workshop brought together researchers and policy-makers from across the globe to discuss midwater habitats as they stand to be influenced by different types of deep-sea resource extraction— polymetallic nodules, massive sulfides, and cobalt crusts— and our conclusions and recommendations were pooled into a public workshop report.

Over the course of the 4-day workshop, we broke into groups to brainstorm the following broad questions, among many others:

1.     What do we know about the biology of oceanic midwaters?

Midwater ecosystems encompass the largest habitat on Earth and are typically defined as the open ocean below 200 meters. They harbor a significant biomass and diversity of animals including plankton, jellies, fishes, and marine mammals. These communities contribute substantially to ecosystem services including carbon transport from the sea surface to deep waters, nutrient supply from deep waters to surface waters, and marine food web connectivity between ocean depths. They also support pelagic fisheries such as those for tuna and billfishes like sailfish and marlin.

Diversity of midwater animals: Squid, fish, shrimp, copepods, medusa, filter feeding jellies and marine worms are among the many midwater creatures that could be affected by deep sea mining. (Photos: © E. Goetze, K. Peijnenburg, D. Perrine, Hawaii Seafood Council (B. Takenaka, J. Kaneko), S. Haddock, J. Drazen, B. Robison, DEEPEND (Danté Fenolio) and MBARI

2.     How might deep-sea mining influence these essential habitats and their communities?

Midwaters are also one of the most poorly studied habitats, and therefore itʻs difficult to know how deep-sea mining will affect the marine environment as a whole. However, mining operations will release discharged sediment plumes into the water column and increase underwater noise as crushed mineral ore is lifted from the deep seafloor all the way to the surface (up to five kilometers, or three miles, in some areas!). These factors will undoubtedly interact with midwater communities, and given their crucial role in oceanic ecosystem function, management regulations and guidelines should be strengthened to minimize their vulnerability.

This diagram shows how sediment plumes and noise generated by deep-sea mining could interact with pelagic communities. (© Amanda Dillon, graphic artist)

3.     What research needs to be conducted to address these unknowns and create effective mining regulations to reduce harm to midwaters?

Studies should focus on increasing our understanding about the biodiversity, behavioral patterns, and species composition of midwater communities, especially those in targeted mining regions such as the Clarion-Clipperton Zone. All participants at the workshop agree that discharge plumes from mining should be released no shallower than depths of 1,500 – 2,000 meters (more or less a mile down) to mitigate disruptions to surface and midwater ecosystem services. Noise-generation from mining should avoid depths between 700 – 1,300 meters (around half to three-quarters of a mile) as these depths encompass the deep sound channel that can easily carry underwater sound for thousands of miles. Overall, we concluded that increased research efforts and a precautionary approach to deep-sea mining management are essential in order to protect midwater habitats from environmental harm.

In light of the growing attention to this topic, a fellow lab member and I were asked to co-author an additional article for the Deep-Sea Mining Observer, which we titled “What impact will deep-sea mining have on midwater habitats?” Together, the articles and reports resulting from our 2018 workshop shed light on just how important, yet unexplored, oceanic midwaters are, and call for strengthened research and management to avoid significant harm to these ecosystems.