Mining the deep ocean floor for valuable metals is both inevitable and vital, according to the scientists, engineers and industrialists exploring the world’s newest mining frontier.

The special metals found in rich deposits there are critical for smart electronics and crucial green technologies, such as solar power and electric cars. But as the world’s population rises, demand is now outstripping the production from mines on land for some important elements.

Those leading the global rush to place giant mining machines thousands of metres below the sea surface say the extraordinary richness of the underwater ores mean the environmental impacts will be far lower than on land. But critics say exotic and little-known ecosystems in the deep oceans could be destroyed and must be protected.

Dozens of exploration licences have already been granted for huge tracts of ocean floor and world leaders, including the G7 nations (pdf), have their eyes on the opportunities. But the rules to ensure the responsible exploitation of this global resource are still being written.

The acid test is set to be the start of commercial sea bed mining, due to begin within two years, 1,600m below waters off Papua New Guinea. There, Nautilus Minerals plans to release three giant crawling machines to grind up rocks rich in copper, zinc and gold and pump the slurry up to a custom-built surface ship at a rate of over 3,000 tonnes a day.

Oceans cover 70% of the planet and are relatively unexplored, says Mike Johnston, Nautilus’s chief executive: “It makes sense to explore this untapped potential in an environmentally sustainable way, instead of continually looking at the fast depleting land resources of the planet to meet society’s rising needs.”

“The seafloor contains some of the largest known accumulations of metals essential for the green economy, in concentrations generally much higher than on land, so it is inevitable that we will eventually recover essential resources from the seafloor,” he said.

Prof David Cronan, a geochemist at Imperial College London, agrees it will happen but is less certain when. “It is an inevitability – it’s just the timing that is in question. For the past 50 years it has been just over the horizon. But in the last five to 10 years there has been a step change – the realisation that marine metals are likely to be useful.”

The drive is not just about ensuring a growing supply of the latest new smartphones, says Bramley Murton, from the UK’s National Oceanography Centre. “It goes much further than that. To make a low-carbon future, we need these [metals] to make the technologies for green energy production. We need these raw materials to enable civilisation to become more sustainable.” He says recycling is worthwhile, but insufficient.

There is also a geopolitical dimension, with some important resources currently monopolised by single nations, such as the rare earth elements (REEs), which have widespread uses in communications, computing and weaponry. “When you get most of the world’s REEs from one country [China], you start asking questions about security of supply,” says Christer Fjellroth, at the National Subsea Research Initiative in the UK.

The focus of Nautilus, and many other players, are seafloor massive sulphide deposits, stadium-size mounds of metal-rich rock deposited by intense hot springs at mid-ocean ridges, which are where volcanic activity forms new ocean crust. These also host unique ecosystems of giant worms, eyeless shrimps, crabs, corals and sponges and newly found vents usually reveal brand new species.

But Murton says: “I don’t think anyone would think of mining active hydrothermal systems. Mining in 400C water is not going to last long, especially when the water has a [highly acidic] pH of one.” Instead, extinct systems are easier targets, though these still host some life.

The other main target of deep sea miners are tennis-ball sized nodules, formed over millions of years and present on much of the world’s seabeds. These can be harvested rather than mined, though a much larger area has to be exploited. “It’s like picking berries,” says Fjellroth. Another possible source is hard cobalt-rich crusts that form slowly in some regions.

China is pursuing all three. Nodules are being targeted in the eastern Pacific, with China’s largest mining company granted an exploration licence for 72,000 sq km earlier in May, crusts in the western Pacific and sulphide deposits in the south-west Indian Ocean.

Hao Zheng, from the Changsha Research Institute of Mining and Metallurgy and part of the Chinese Ocean Mineral Resources R&D Association, which brings together hundreds of researchers, says a trial mining system is due to deploy in 2020, to crush and recover ore nodules from the South China Sea.

“We have found some major nodules on the seabed there,” he says. The seabed crawler being built is a few metres in size, far smaller than the commercial-scale machines Nautilus commissioned from UK company SMD. “They are like Transformers!” he said.

The deep sea gold rush is also attracting the attention of other companies with long experience of offshore operations. BP did its first trial of an autonomous underwater vessel dubbed Squirrel in December, which can be dropped from a drone and is intended to be a “rapid strike vessel” for inspecting operations, says Joe Little, who works in the company’s chief technology office.

BP has also recently combined a small remotely operated vessel with a magnetic crawling device – called robodiver – to inspect pipes in Angola, Little told a deep sea mining summit in London. The fast rise of artificial intelligence could also be used, according to Simon Wenkel, at Clausthal University of Technology in Germany: ” It could be something like swarm robotics.”

New technologies could help monitor the environmental impact of mining and with the international regulations still being drafted, all observers agree there is the opportunity to get strong protections in place before exploitation begins, unlike in many cases on land. “Most mining operations on land did a very bad job in the past,” says Wenkel. But he warns: “Zero impact mining is not possible unfortunately.”

“Mining will be the greatest assault on deep-sea ecosystems ever inflicted by humans,” according to hydrothermal vent expert Verena Tunnicliffe, at the University of Victoria in Canada. She argues that active vents must be off-limits for mining to protect the new knowledge and biotechnology spin-offs they can deliver and strict controls must be in place elsewhere: “This gold rush needs some strong traffic control in regulation.”

Others, such as Rakhyun Kim at Utrecht University in the Netherlands, go further: “The global community should question and scrutinise the underlying assumption that deep seabed mining is going to benefit humankind as a whole before commercialising the common heritage of humankind.”

In 2016, a region in the Pacific being explored for polymetallic nodules by a UK subsidiary of Lockheed Martin was revealed as having “one of the most diverse communities” recorded in the deep ocean.

“The questions are big and the answers are unknown,” says Murton, on the impact mining could have on deep sea ecosystems. But he says the ecosystems must be fairly robust. “Every now and again they are obliterated by a lava flow and the vents also explode from time to time.”

Johnston, from Nautilus, says: “Reclamation by nature is expected to occur relatively quickly following the cessation of mining. This is as observed for naturally disturbed sites on the East Pacific Rise where researchers have documented the re-establishment of a site within five to 10 years, after being completely obliterated by a single volcanic event.”

“Everyone is watching anxiously for Nautilus,” says Henk van Muijen, at Royal IHC, a Dutch marine engineering firm. “If that goes wrong it will give a setback to deep sea mining.”

Conversely, if Nautilus successfully bring up valuable metals, “that is when you will see things taking off”, says Tracy Shimmield, at the British Geological Survey. She argues that the UK should seek a national licence from the International Seabed Authority in order to set up an ocean floor observatory, which could both test new mining technologies and monitor their the environmental impacts.

Companies backed by Russia, Germany, France, Portugal, South Korea, Brazil and more are all pushing ahead on deep sea mining and almost all of the Atlantic ridge from the equator to the Arctic circle has been claimed in recent years. Now Norwegian researchers are exploring the seafloor deep into the Arctic circle and have found several new vent systems near Jan Meyen island.

“I think there is huge potential,” says Filipa Marques, at Bergen University, adding that Norway’s 40-year history of offshore oil and gas puts it in a strong position to exploit the resources.

Most of the people involved in deep sea mining expect large-scale commercial production in about a decade, with companies seeking to benefit from the experiences of Nautilus. “Everyone is racing to be second,” says Fjellroth.

Whether the scientific knowledge and regulations are in place by then to ensure deep sea mining does not repeat the devastation of many mines on land remains to be seen, although the G7 leaders say: “We are committed to taking a precautionary approach.”

For Murton, tellurium is a good example. It is a key metal for high performance solar panels and is 50,000 times more concentrated in deep sea deposits than in land ores. “Because the grades are so much higher, there is much less impact. Deep sea mining is the lesser of two evils.”