There is treasure in the sea, and much of it lies in plain view on the deep ocean floor. Fields of metallic nodules and towering hydrothermal chimneys accumulate precious and industrially prized metals, estimated to be worth many billions to even trillions of dollars.
It is there for the taking, and mining operations around the world are exploring strategies to plunder this treasure, asserting that mining in the deep sea is more sustainable and less harmful than doing so on land. Mining explorations covering more than 500,000 square miles have been approved by the International Seabed Authority, which regulates mining in international waters. That’s roughly twice the size of Texas.
But the deep sea is not a barren, lifeless wasteland, as once thought. Exploration in recent decades has revealed thousand-year-old corals, microbes that can treat cancer and infectious diseases, and hydrothermal vent fields of monumental proportions, from which living creatures convert sulfur and methane into energy, offering a glimpse at the origins of life on earth. So the challenge is not simply finding the X on the treasure map, but bringing the materials to the surface in a way that inflicts minimal damage to the ocean environment.
As deep-sea biologists who study the drifting and swimming inhabitants of the ocean, we originally felt that any resulting harms from deep-sea mining would primarily be felt at the bottom of the sea. Nearly all of the environmental impact studies on deep-sea mining have focused on the seafloor, where the aftermath is visible for decades. Seabeds are still denuded 30 years after experimental mining machines passed by.
But as we and our colleagues noted recently in the journal Proceedings of the National Academy of Sciences, mining will have pronounced and debilitating impacts that will be felt not just on the seabed but also throughout the deep water column, which extends from about 600 feet below the surface to the seafloor, where the extraction takes place.
Minerals that miners seek form and accumulate extremely slowly in the deep ocean, with growth rates of only a few millimeters per million years. A nodule the size of a tennis ball lying on the sea floor and consisting largely of prized rare-earth metals could be more than 14 million years old. While the ecosystem might recover to some extent after a hundred years, the mineral resources will never be replaced. Mining serves present-day consumers but leaves the environmental consequences for their children and grandchildren.
Critically, what is missed in assessments of mining impacts is the effect on the ocean itself. The sea is not just the seafloor alone, but also what lies above it: roughly 13,000 feet of water on average, more than twice as deep as the deepest point of the Grand Canyon and including more than 90 percent of the planet’s life-sustaining habitats. This deep mid-water ecosystem — from microbes and worms to jellies and giant squid — is important and is linked to us in many ways.
When a nodule is gouged and vacuumed from the seafloor, it is pumped to a surface ship through a pipeline. The minerals are removed, and then the muddy, silty, toxin-enriched fluid is pumped back into the sea as what is called a “dewatering plume.” Heavier particles will sink to the seafloor but must pass through thousands of feet of intervening water before settling. Additionally, the fine silt will drift and flow for miles and months in the ocean currents. It is frightfully clear that the impact of this drifting plume on open-water ecosystems will be severe, varied and global in scale.
Decades of deep-sea science have taught us that organisms in the deep water have adaptations that make them especially susceptible to these mining impacts. Many of them feed on small particles that flake down from the surface, as if in a giant snow globe. These filter-feeders are not limited to worms and snails, but also include the vampire squid and 30-foot-long gelatinous chains called salps. This process of consuming particles contributes to the flow of carbon from the atmosphere to deep sediments in the ocean, helping regulate the earth’s climate.
We’ve seen that the food web is complex and interconnected, linking ultimately to commercial fisheries worth billions of dollars. Any toxins in the environment or diet of these fish will end up on our dinner plates. Amazingly, about three-quarters of the animals in the water column can make their own light, and they use this bioluminescence to find prey and mates, while avoiding predators by using glowing camouflage as a cloaking device.
As a result of the mining, animals already living near their physiological limits would be eating mouthfuls of poisonous dirt for breakfast, respiring through clogged gills and squinting through a muddy haze to communicate.
Based on predicted discharge rates, a single mining ship will release between two million and 3.5 million cubic feet of effluent every day, enough to fill a fleet of tanker trucks 15 miles long. Now imagine this process running continuously for 30 years — the lifetime of a mining lease. Most important, these sediment plumes will not respect the neat boundaries defined by a permit. Regulatory buffer zones set up around the Cook Islands, for example, extend only 50 nautical miles — insufficient to protect their reefs, fisheries and tourism from these expanding sediments, which are projected to travel hundreds of miles.
The companies and governing agencies that stand to profit from mining activities are based in the United States, Canada, Europe and Asia. They are geographically, politically and economically removed from the small island nations that will bear the brunt of the consequences. While government leaders may welcome mining for economic gain, it is the Indigenous people and local communities on these islands who are often without a meaningful voice in decisions that will weigh heavily on their future. In the United States, which is not a member of the nearly 170-nation seabed authority, the Trump administration is exploring whether it can open portions of existing national marine sanctuaries to mineral extraction.
Most deep-sea mining plans predict plume discharges to be located around 3,300 feet down, even when mining operations are taking place on a seabed more than 16,000 feet deep. This may be out of sight from the surface, but it is not deep enough to avoid potentially disastrous effects on deep-ocean ecosystems and food webs. When mining operations commence, companies must shoulder the additional expense of depositing their effluent as close to the original seafloor disturbance as possible. Doing so will minimize harmful effects of both the sinking and drifting plumes on water-column life and reduce their spread to nearby ecosystems.
Historically the deep sea has been considered remote and largely devoid of life, and to have an inexhaustible capacity to absorb our pollution. In reality, these deep water ecosystems are fragile, diverse and connected to us. Mining operations must reduce their impact on the whole of the ocean and not just the seafloor. The dazzling treasure of oceanic biodiversity has unfathomable value as well.