A few years ago, a senior executive from a deep-sea mining company gave a presentation in a conference room at a mining industry event in London. The presentation began with pictures of Indonesian open-pit nickel mines, with red laterite soil scraped to the horizon, an orange river flowing downstream, and communities forced off their land to make way for extraction. Then he clicked to a different picture of the deep ocean, which was dark and seemed to be featureless, displaying nothing but a huge, peaceful body of water. The argument was the contrast. He asked, “Would you prefer this or that?”
The deep-sea mining sector has been honing this comparison for years, and it has some validity. There are established environmental and human costs associated with land-based mining for manganese in numerous African countries, nickel in Indonesia and the Philippines, and cobalt in the Democratic Republic of the Congo. The impacted communities are actual. It is evident that the habitat is being destroyed. It is possible to measure the pollutants. In contrast, most people cannot see the deep water, making its ecological significance more difficult to convey and more likely to be disregarded.
However, the claim that deep-sea mining is better for the environment than land-based mining necessitates adopting a number of assertions that are inconsistently supported by the scientific literature. The first is that disturbances to the seafloor are transient and reversible. The IOM and OMCO experimental tracks in the Clarion-Clipperton Zone, which tracked the aftermath of small-scale test mining operations in the 1970s and 1980s, revealed that sediment disturbance persisted decades later and that the benthic communities in impacted areas had not returned to baseline even forty years after the initial disturbance. Sponges, corals, worms, and xenophyophores are among the creatures that grow on and around polymetallic nodules on the abyssal plain at a rate of millimeters per thousand years. They would be eliminated by commercial mining over thousands of square kilometers. The recuperation period is not human, but geological.
The issue that causes harm outside of the immediate mining area is the sediment plume. Fine sediment particles are suspended in the water column as a vehicle scrapes nodules from the seafloor. The bioluminescent creatures and filter feeders that are essential to the mid-water column ecosystem are suppressed by these particles, which can move hundreds of kilometers with ambient currents before settling. Compared to early industry forecasts, the plume impacts observed in current test operations have been bigger and more lasting. The cumulative footprint of a commercial-scale mining operation would be significantly bigger than the area directly extracted, according to more recent modeling that incorporates better current data.
The ecological discussion becomes overtly political when it comes to the greenwashing claim that deep-sea mining is an essential part of the clean energy transition. The argument goes like this: deep-sea mining is environmentally justifiable as part of the fight against climate change since electric vehicles require lithium-ion batteries, which require cobalt and nickel, which are abundant in polymetallic nodules. Five years ago, this argument was stronger than it is today. Lithium iron phosphate batteries, which are already common in many Chinese-market EVs and increasingly in goods worldwide, contain no cobalt.
Battery technology has been evolving toward chemistries that decrease or eliminate cobalt. More advanced than most people think, sodium-ion batteries have the potential to significantly lower the demand for nickel. The market has been shifting away from the particular minerals that deep-sea mining companies have based their business models on, and the mineral requirements of the clean energy transition are not fixed; rather, they depend on whatever technologies succeed in the market.
The argument that receives the most attention from ecologists and materials scientists and the least attention from industry-facing media is the circular economy option. The metals that end-of-life EV batteries, abandoned electronics, and industrial waste streams now contain are the same metals that deep-sea mining aims to harvest from the ocean floor. In comparison to its promise, urban mining—the methodical extraction of metals from e-waste—remains remarkably underdeveloped. The argument that primary extraction from the seabed is required is complicated by estimates of the amount of material recoverable from current waste streams if processing facilities were constructed at scale.
