For a sustainable future, it’s widely accepted that the global population needs to move away from fossil fuels. While electric looks to be a suitably green alternative, it comes with one major flaw: there just aren’t enough metals to make the shift. We can get more metals by mining, something we’ve done for thousands of years – but considering the costs of ripping up forests and displacing wildlife to reach it, does the battery revolution still count as a green alternative?

What if we could access the metals needed to make batteries some other way? One possible alternative is to move mining to the deep sea, where precious nodules known as manganese tubers can be found laying on the seabed as loosely as pebbles on the sand. 

We covered these metal-rich nuggets, sometimes referred to as “deep sea potatoes”, back in April, and after seeing our coverage The Metals Company (TMC) reached out to see if we’d like to hear how their research is going. It was a yes from us, and it seems there’s little doubt surrounding their material potential in the transition to a greener future.

“90 percent of the world's exploration contracts for nodules are in the Clarion-Clipperton Zone, which represent less than half of 1 percent of the global seafloor,” TMC PR and Media Manager Rory Usher told IFLScience. “But this represents the largest source of manganese, nickel, and cobalt, anywhere on the planet and that dwarfs everything on land by many orders of magnitude. There are enough metals in situ at two of the sites that would satisfy the needs of 280 million cars, which represents every car in America, or a quarter of the world's vehicle fleet.”

At a time when the value of Earth's ecosystem services could outperform carbon credits in the fight for our future, perhaps it's time to move in a new direction. Mining the deep sea isn't without its environmental and logistical complications, but as a global network of researchers is discovering, taking the plunge could well be worth it.

Is deep-sea mining as bad as terrestrial mining?

“I've been implementing an environmental impact assessment like you would do for any mining project,” said environmental manager for TMC Dr Michael Clarke, who after years working on environmental impact assessments for terrestrial mines has now moved to studying the impacts of mining the deep sea. “The only difference is that this one is in the middle of the Pacific Ocean, a five-day sail from the nearest port at [a depth of] 4,000 meters [13,123 feet].”

That depth is a crucial point in the pursuit of manganese nodules, because pitted against terrestrial mining sites there’s comparatively very little life in the benthos. TMC told IFLScience there are 13 grams [0.46 ounces] of biomass per square meter on the abyssal seafloor, whereas in the rainforests of Indonesia (one of the leading countries for metal mining) you’re looking at closer to 30 kilograms [66 pounds] of biomass per square meter.

Accessing metals from terrestrial sites means clearing forests, habitats, and ecosystems, making them vulnerable to erosion that can contribute to runoff, which ends up in the ocean. We know rainforests are biodiversity hotspots, and themselves act as a carbon sequestration tool, so what about the seafloor?

Academics across the globe have been researching life in the benthos to try and better understand this, hailing from institutions such as London’s Natural History Museum, the National Oceanographic Centre in Southampton, Heriot-Watt University in Scotland, the University of Leeds, the University of Bremen, the University of Hawaii, Texas A&M University, and the University of Maryland, among others.

What they’ve discovered is that while there is life on and around the nodules, including some larger animals, most of it is microscopic. Some of the earlier press directed at deep-sea mining has warned of the risk of mass-extinction events often using imagery of wildlife from shallower water to demonstrate potential victims, but given the already great cost of mining on land it becomes a balancing act of where the greater harm lies.

“A lot of people have a real misconception of what the seabed looks like at 4,000 meters depth,” said Clarke. “There is life down there, there's no doubt about it, but it's not as abundant as is often portrayed.”

How can we establish the impacts?

Of course, just because life is small doesn’t mean it isn’t important, which is why TMC have been gathering baseline and collection data to establish the CCZ’s conditions and what impacts their approach might have. These datasets are the two main components of an environmental impact assessment, and the results go to the International Seabed Authority regulator to decide if risks are acceptable. 

“Our own baseline studies took three years and then we did the collector test, which is where we built a system that actually collects the nodules,” explained Clarke. “This went out in the latter part of last year, and we collected approximately 3,000 tonnes of nodules.”

The project eventually aims to collect 1.3 million tonnes of nodules a year, so the impact insights yielded from these tests will be monitored over time and scaled up to get a clearer picture of how deep-sea mining in the CCZ will realistically influence the environment.

The key areas of concern center around what impact the plume created by the collectors might have, both when dislodging the nodules from the seabed with a jet of water, the sediment released as the nodules are filtered around, and that which gets dropped in the midwater when the nodules are transported to the surface. Sediment might not sound terribly dangerous, but the concern was that it might create dust storms that could travel long distances and choke small organisms.

"These particles could feasibly clog the feeding apparatus of these organisms for an area spanning hundreds of square kilometers from the point where the plumes generated,” said Clarke. “What we're actually finding when we go out there and do the tests is that the sediment goes into the vehicle and comes out the vehicle, forming what we call a turbidity flow. It behaves more like a liquid than a gas and doesn't rise much more than 2 or 3 meters [6.6 to 9.8 feet] above the back of the collector. So, it doesn't create the huge dispersive plumes that would be required for the sediment particles to travel hundreds of square kilometers and impact organisms over a huge area.” 

The plume generated at the midwater could feasibly have had the same impact, but tests have shown it’s very dilute. 

“You only have to get a few hundred meters away for it to dilute around 1,000 times and to become really hard to even find the sediment,” Clarke continued. “So, we really don't think there's much potential for these midwater sediment plumes to spread out over large areas either.”

These findings have been replicated in studies conducted by MIT and Global Sea Mineral Resources, which has left TMC feeling confident that they can contain the impacts of deep-sea mining.

No perfect solution

There’s no getting away from the fact that we don’t currently have enough metals in circulation for recycling to supply enough energy transition metals given the amount we need for the green transition. These source metals need to come from somewhere, so we’re faced with the dilemma of working out which approach has the best yield-to-impacts ratio. 

At present, 50 percent of the nickel market comes from Indonesia, where rainforest is flattened to make way for operations. This land is used by both humans and wildlife, so its absence is very apparent and its recovery is slow due to ongoing use. By comparison, after a collector has scooped up the nodules from the seabed, it can recover more quickly because little activity is going on here. 

While these nodules do take millions of years to form, the argument that once it’s gone – it’s gone – is true of any source metal. On the other hand, only one option requires the ripping up of carbon-sequestering rainforest to reach it.

Carbon has been raised as a concern around deep-sea mining, as much of it is stored in sediments, but TMC explained that at present there’s no known mechanism through which this could rise to the surface. A 2020 study actually found that using nodules puts 94 percent less sequestered carbon at risk and reduces emissions by up to 80 percent depending on the specific metal. 

The nodules also come with the added benefit of a much higher grade, meaning harvesting them has a higher yield, so less time is needed to collect the same volume of source metals compared to a terrestrial operation. If given the go-ahead, the life of TMC’s first project, NORI-D, would only continue until 2046 (lasting around 25–30 years) to inject just enough metals into the system to enable the circular economy. NORI-D was also estimated by a third-party expert to outperform land-based routes of producing nickel, copper, and cobalt in almost every impact category analyzed.

It goes without saying that any endeavor that disrupts an environment should be approached with enormous caution, but at a time when the planet’s future rests on reducing our carbon footprint, it could be that a short walk along the seafloor is less damaging to the planet than a decades-long dig in our few remaining green spaces.

“Existing mining has a lot of intelligent people working on reducing impact, but they are up against one of the immovable forces on the planet, geology,” concluded Usher. “You can't escape the fact that grades are so low and falling, which means you can't escape producing ever increasing quantities of waste.”

“We can reduce the carbon footprint of these metals by up to 90 percent at a time when combatting the climate crisis is most front of mind. In addition, we’re not ripping down carbon sinks, like in Indonesia and the Democratic Republic of Congo. When you rip down the forest, you remove an ecosystem that could have sequestered carbon for hundreds of years.”

You can find out more about The Metal Company’s research into deep-sea mining on their website.