Photo by Naomi August
Deep-sea mining operations could severely disrupt marine life in the ocean’s “twilight zone” by replacing nutritious food particles with sediment “junk food,” according to the first study to examine the impact of mining waste on this critical ecosystem.
Research published in Nature Communications found that 53% of all zooplankton and 60% of micronekton in the twilight zone—a vital region 200 to 1,500 metres below sea level—would be impacted by waste discharged from deep-sea mining operations in the Pacific’s Clarion-Clipperton Zone (CCZ).
The study, led by researchers at the University of Hawai’i at Mānoa, examined water samples from a 2022 mining trial and found that discharged particles had far lower concentrations of amino acids—a key indicator of nutritional value—than naturally occurring particles that sustain life at these depths.
Michael Dowd, lead author and oceanography graduate student, said: “When the waste released by mining activity enters the ocean, it creates water as murky as the mud-filled Mississippi River. The pervasive particles dilute the nutritious, natural food particles usually consumed by tiny, drifting zooplankton.”
Jeffrey Drazen, co-author and oceanography professor, explained: “Our research suggests that mining plumes don’t just create cloudy water—they change the quality of what’s available to eat, especially for animals that can’t easily swim away. It’s like dumping empty calories into a system that’s been running on a finely tuned diet for hundreds of years.”
The twilight zone hosts diverse life including krill, fish, squid, octopus and gelatinous species. Many organisms travel upward to the surface each night to feed, then descend by day, transporting carbon to the deep ocean in a process critical to ocean and human health.
Erica Goetze, co-author and oceanography professor, said: “This isn’t just about mining the seafloor; it’s about reducing the food for entire communities in the deep sea.”
The study examined operations targeting polymetallic nodules containing critical minerals including cobalt, nickel and copper. During the process, nodules are pumped to surface vessels where they’re separated from waste material. The leftover sediment must be returned to the ocean, with some operators proposing discharge within the twilight zone.
The findings raise urgent concerns about system-wide effects if large-scale commercial mining proceeds without environmental safeguards. Pacific tuna fisheries operate in the CCZ, meaning deep-sea mining waste could impact fish on dinner plates globally.
Brian Popp, co-author and earth sciences professor, said: “Deep-sea mining has not yet begun at a commercial scale, so this is our chance to make informed decisions. If we don’t understand what’s at stake in the midwater, we risk harming ecosystems we’re only just beginning to study.”
The findings underscore a major regulatory gap, as no international rules currently govern where or how mining waste can be discharged. The authors hope their findings will inform decisions by the International Seabed Authority and NOAA, which reviews environmental impacts of US-led deep-sea mining initiatives.
In April 2025, President Trump signed an executive order directing NOAA to expedite the permitting process for companies to mine the ocean floor. Last month, NOAA sent a draft rule to the White House to streamline operations.
Sheryl Murdock, a deep-sea researcher at Arizona State University not involved in the study, said: “There’s a lot more research that needs to be done to be able to make an informed decision about how to manage this industry, if it does start, in a way that will prevent, essentially, serious harm to the ocean and ocean ecosystem.”