A new study reveals that sediment plumes from deep-sea mining could starve vital marine life in the ocean's twilight zone by replacing nutritious particles with nutrient-poor waste. Researchers from the University of Hawai'i at Mānoa found that this 'junk food' effect threatens zooplankton and micronekton, potentially rippling through the entire ocean food chain. The findings, based on a 2022 mining test in the Clarion-Clipperton Zone, highlight risks to ecosystems supporting global fisheries and carbon cycles.
Published on November 6 in Nature Communications, the study from the University of Hawai'i (UH) at Mānoa provides the first direct evidence of deep-sea mining's impact on the midwater twilight zone, a layer between 200 and 1,500 meters deep in the Pacific Ocean's Clarion-Clipperton Zone (CCZ). This region, spanning 1.5 million square kilometers licensed for mineral exploration, is rich in polymetallic nodules containing cobalt, nickel, and copper—minerals essential for electric vehicles and renewable technologies.
During mining, nodules are collected from the seafloor with surrounding sediments and seawater, then separated on surface vessels. The resulting waste, including fine sediment and nodule fragments, is discharged back into the ocean, often proposed for release in the twilight zone. Analyzing samples from a 2022 mining test, scientists discovered that these plumes create murky water, diluting natural food particles with low-nutrient mining sediment.
"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," said lead author Michael Dowd, a graduate student in oceanography at UH Mānoa's School of Ocean and Earth Science and Technology (SOEST).
The research showed that mining particles contain far fewer amino acids—a key nutritional measure—than natural detrital particles. Consequently, 53% of zooplankton and 60% of micronekton, small swimming animals like shrimp and fish that feed on zooplankton, could be affected. These organisms form the base of the food web, supporting larger predators including tuna, seabirds, and marine mammals. Many twilight zone species, such as krill, squid, and jelly-like creatures, undertake daily vertical migrations, aiding carbon sequestration.
"This isn't just about mining the seafloor; it's about reducing the food for entire communities in the deep sea," said co-author Erica Goetze, a SOEST oceanography professor. "We found that many animals at the depth of discharge depend on naturally occurring small detrital particles—the very food that mining plume particles replace."
Co-author Jeffrey Drazen, a SOEST deep-sea ecologist, added: "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 study underscores regulatory gaps, as no international rules govern waste discharge depths. Authors urge the International Seabed Authority and National Oceanic and Atmospheric Administration to consider these impacts before commercial mining begins, potentially affecting global fisheries like tuna that migrate through the CCZ.
"Deep-sea mining has not yet begun at a commercial scale, so this is our chance to make informed decisions," said co-author Brian Popp, a SOEST Earth sciences professor. "If we don't understand what's at stake in the midwater, we risk harming ecosystems we're only just beginning to study."