Race to the bottom: Deep-sea mining, explained

Posted: June 30, 2025

More than 150 years ago, the British warship HMS Challenger set sail to circumnavigate the globe, crossing the Pacific, Atlantic and Southern Oceans in a voyage lasting more than three years. Despite appearances, it was no military expedition; in fact, it marked a pivotal moment in our understanding of the sea and the first comprehensive effort to explore its deepest depths.

The six-person scientific team aboard the ship, led by Charles Wyville Thomson, a Scottish naturalist, took hundreds of measurements and countless samples throughout the trip—proving that the deep sea was neither a featureless expanse nor covered in primordial ooze, as some believed at the time.

In exploring the ranges, trenches and plains far below the surface, Thomson’s team also made a lesser-known discovery: on March 7, 1873, its dredge hauled up “several peculiar black oval bodies.” Together with the rest of the expedition’s collections, the rocks were likely sent back to England for further study.

Now, those same peculiar black ovals could represent the mining industry’s next frontier.

Why deep-sea mining is gaining momentum 

Those oval bodies are polymetallic nodules, and they can be found in vast numbers scattered across the deep ocean’s abyssal plains, as far as 6.5km below the waves. 

Once upon a time they could have been shark teeth or tiny shells. As they sank to the bottom of the ocean, they were gradually covered by layers of manganese and other metals over millions of years. 

Because of this process, these potato-sized lumps are now prized as a potential critical resource to fuel the energy transition. The metals they contain—which also include cobalt, nickel and copper, as well as traces of lithium and rare-earth elements like yttrium—are found in everything from electric vehicles to batteries to power lines (not to mention cellphones and other electronics). 

Aside from polymetallic nodules, there are two other main sources of minerals that could be mined in the ocean: 

• Cobalt-rich ferromanganese crusts, which form at the flanks of seamounts and underwater ridges, at depths of 800 meters to 2.5 kilometers. Like the nodules, they primarily contain manganese, cobalt, nickel and copper. 
  
  
• Massive sulphide deposits, which are found near active and inactive hydrothermal vents, between 1km and 4km below the surface. They also contain copper, as well as zinc, silver and gold. 

Why go to the trouble of mining the deep sea? By some estimates, demand for critical metals and minerals is set to keep growing for decades. 

The International Energy Agency predicts that, to reach net zero emissions by mid-century and limit global warming to 1.5 degrees Celsius, we will need 50% more copper by 2040—plus twice as much nickel, cobalt and rare earth elements, and up to eight times the amount of lithium currently produced. 

And, as it turns out, subsea deposits of the most coveted metals needed for the energy transition are thought to be much more plentiful than land-based reserves. Aside from sheer abundance, proponents argue that deep-sea mining could also circumvent issues plaguing terrestrial mining, including deforestation, waste pollution and labor conditions. 

On the other hand, critics of deep-sea mining warn that trawling the seafloor could harm some of the earth’s least understood ecosystems or initiate maritime disputes over everything from subsea cables to fishing rights. There are also questions whether it will be commercially feasible. 

Future demand is unpredictable, too. The IEA itself says that better recycling, as well as innovative technologies and changes in consumer behavior, could reduce primary demand for many critical minerals by as much as 30%. 

How deep-sea mining would work 

One of the most promising areas for exploration is the Clarion-Clipperton Zone, several million square miles of otherworldly abyssal plain that lies between Hawaii and Mexico.  

At this depth, the seafloor is shrouded in near-constant darkness, lit up only by flashes of bioluminescence. Strewn atop and buried within its muddy clay lie trillions of polymetallic nodules. By some estimates, they contain more nickel, manganese and cobalt than all terrestrial reserves combined. 

To date, mining at such depths has only occurred in small tests. At commercial scale, it would likely involve fleets of remotely operated vehicles that vacuum up rocks and send them up chutes to ships waiting at the surface, which would pump surplus sediment back into the sea and transport the ore to shore for processing. Some of the bottom-trawling vessels could hover just above the ground, to avoid churning up too much of the seafloor. 

In addition to a suction- or hydraulics-based collection system, the vehicles would come equipped with thrusters and tracks to move both in the water and on the seafloor. Cables and a riser to lower the vessel and transport the nodules would sit at the top, while a buoyancy system would reduce the load on the vehicle structure.
Aside from on-the-ground logistics, companies also have to worry about seabed mapping—since just over one-quarter of the global seabed has been charted in detail so far. This is done using sonar technologies that send out acoustic waves, which reflect off the sea floor to indicate depth and topography.

Companies are now using artificial intelligence to process that data in real time, allowing surveyors to view it on board or remotely even as surveys are underway. 

What’s next for deep-sea mining? 

Countries are free to pursue deep-sea mining in their own domestic waters. Norway became the first in the world to greenlight commercial deep sea mining in its own waters last year, but later withdrew the licenses due to opposition within its governing coalition (preparatory work nonetheless continues). 

But more than half of the world’s oceans, and the majority of their mineral deposits, are instead governed by the International Seabed Authority, a UN-affiliated body made up of 169 member states and the European Union. 

This year, diplomats meeting under the ISA’s auspices hope to finalise a framework for deep-sea mining that would clarify rules around taxation, royalties and environmental impact, as well as sanctions for non-compliance. 

Dozens of contractors and their country sponsors are already waiting in the wings: to date, the ISA has signed 31 exploration contracts—half of them for polymetallic nodules in the Clarion-Clipperton Zone.

While Thomson and his team of scientists made countless groundbreaking discoveries aboard the Challenger, they could have hardly imagined the future potential of those peculiar black ovals they hauled up to the surface.