Between 200 and 1,500 meters below the ocean’s surface lies a vast, dimly lit world known as the twilight zone — home to krill, squid, and countless drifting animals that quietly sustain life all the way up to tuna, seabirds, and marine mammals. This hidden ecosystem runs on a finely tuned diet of nutrient-rich particles that drift down from sunlit waters above.
Now, a study published in Nature Communications has found, for the first time, that sediment discharged during deep-sea mining operations floods this zone with nutritionally empty particles — effectively replacing natural food with what researchers call “junk food” sediment.
A hidden ecosystem under threat
The twilight zone is one of the ocean’s most productive yet least studied habitats. Stretching from 200 to 1,500 meters below the surface, it supports enormous populations of zooplankton — tiny drifting animals that form the foundation of the marine food web. Micronekton, including small shrimp and fish, feed on those zooplankton, and larger predators like tuna, seabirds, and marine mammals feed on them in turn.
Many twilight-zone species migrate vertically every night, rising toward the surface to feed and descending again by day. That daily movement transports carbon deep into the ocean, helping regulate the planet’s climate. Sitting at the center of growing industrial attention is the Clarion-Clipperton Zone (CCZ) — a vast stretch of the central Pacific studded with polymetallic nodules rich in cobalt, nickel, and copper, minerals in high demand for electric vehicles and renewable energy technology.
What mining waste actually looks like underwater
Extracting those nodules is not a clean process. Machinery scrapes them from the seafloor along with surrounding sediment and seawater, then pumps everything to a surface vessel. The nodules are separated, and the leftover waste — fine sediment and nodule fragments — gets discharged back into the ocean. Some companies have proposed releasing this waste directly within the twilight zone.
Lead author Michael Dowd described the result in concrete terms: the discharged plumes create water “as murky as the mud-filled Mississippi River.” That turbidity is not simply a visibility problem. It dilutes the nutritious particles that twilight-zone animals depend on. Until this study, the ecological consequences of mid-water discharge were largely unknown, even as approximately 1.5 million square kilometers of the CCZ were already licensed for exploration.
The ‘junk food’ effect: first direct evidence
The research team analyzed water samples collected from depths where waste was discharged during a 2022 mining test in the CCZ. Their central finding was stark: mining particles contained far fewer amino acids than the natural particles that normally nourish marine life. Amino acid content is a recognized measure of nutritional quality.
The study estimates that 53% of zooplankton and 60% of micronekton would be exposed to mining waste discharge. For those animals, the plume displaces their food with something considerably less nourishing. Co-author Erica Goetze put it plainly: “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.”
Ripple effects through the food chain
Disruption at the base of the food web does not stay contained. Stress on zooplankton cascades upward to micronekton, then to the larger predators that depend on them. Tuna migrate through the CCZ, which means nutritional disruption in that zone could eventually affect seafood supplies consumed around the world.
Co-author Jeffrey Drazen framed the broader concern plainly: “It’s like dumping empty calories into a system that’s been running on a finely tuned diet for hundreds of years.” The vertical migration of twilight-zone species also moves carbon into the deep ocean — and disrupting those migrations could reduce the ocean’s capacity to absorb atmospheric carbon, a consequence that extends well beyond fisheries.
A regulatory gap at a critical moment
Despite the scale of mining interest in the CCZ, no international rules currently govern where or how mining waste can be discharged. Policy discussions are underway at the International Seabed Authority, and NOAA is conducting its own environmental reviews. The study’s authors intend their findings to inform both processes directly.
Co-author Brian Popp identified the window that still exists: “Deep-sea mining has not yet begun at a commercial scale, so this is our chance to make informed decisions.” The authors call specifically for rules governing discharge depth before mining scales up. As Drazen noted, the impact of waste plumes varies with depth — getting that decision wrong could cause harm across the entire water column, from surface to seafloor. The science now exists to guide that choice. Whether policymakers act on it is another matter entirely.