An area of sea floor between Hawaii and Mexico is rich in the critical minerals needed to build batteries.

But the Clarion-Clipperton Zone (CCZ) is also rich in marine life — much of it virtually unknown to science, according to new research published today.

Seventeen mining exploration licences cover about one-fifth or 1.2 million square kilometres of the Clarion-Clipperton Zone, with international interests eying off its abundant manganese, nickel, copper and cobalt  deposits.

A complex chemical process has coalesced the minerals into highly pure "potato-sized" nodules that sit untethered in the sediment on the sea floor.

A new study published in Current Biology has found there are more than 5,000 species in the zone that are yet to be formally identified. Many are small — just a few millimetres in size.

Underwater surveys, the bulk of which have been done over the past decade, have brought back samples of species from across the region.

The large majority of those have been recorded informally in databases or in journals, according to study lead author Muriel Rabone of the Natural History Museum London.

"A lot of the work in the CCZ has been done by taxonomists and specialists ... and in these publications they've been recorded as an undescribed species and they're given these [holder] names.

"Because of the sheer practicalities of taxonomic work, this happens a lot."

For their study, Ms Rabone and colleagues trawled those publications and databases, sifting out the double-ups to put some numbers on the flora and fauna found so far within the CCZ.

The number they've come up with is 438 formally classified species, and 5,142 species that are essentially new to science.

And there are likely to be far more species yet to be collected, Ms Rabone said.

"Life evolved in the deep sea and there's this deep evolutionary diversity at the roots of the tree — all phyla are represented in the sea.

"We think [the total number of species] is probably like 10,000-plus, but it's very difficult to say. I mean, some colleagues think it's like 20,000 – 50,000. Taxonomists who work in the region think it's in that kind of order."

'A much better way of doing this'

In what's been called a "sustainability paradox",  we need to deal with climate change, but mining the minerals for clean energy comes with its own suite of environmental risks.

The CCZ is an area of about 6 million square kilometres, between Mexico and Central America to the east, and Hawaii and Kiribati in the west.

Canada-based The Metals Company is one with its sights set on the riches several thousand metres below the ocean surface.

Last year, a subsidiary of The Metals Company was the first to be granted a mining trial approval by the International Seabed Authority (ISA).

Michael Clarke, the environmental manager of The Metals Company, said a big part of his motivation for joining the company was environmental — given the role the minerals will play in addressing climate change.

He said mining in the CCZ could be done with very low impact compared with terrestrial mining.

"The estimates are we're going to need five times more of the critical metals to fuel the green transition than we've got now. Where's that coming from? Take nickel for example, it's almost all coming from Indonesia," Dr Clarke said.

"I used to work on a copper mine in Indonesia that was practising deep-sea tailings placement. Basically you go in there, you cut the rainforest down, you take all the tailings, put them in a pipe at 5,000 metres and dump them in the Coral Triangle [a marine area located in the western Pacific Ocean].

"When The Metals Company contacted me and told me what they were doing I was like 'Wow, this looks like a much better way of doing this than what we're doing in Indonesia at the moment'. So personally that was my motivation."

A 'vacuum cleaner' on the ocean floor

The process for extracting the deep-sea metallic nodules uses a machine that Dr Clarke describes as a "Dyson vacuum cleaner".

The nodules are sucked from the sea floor and transported to the mothership around 4,000m above, via a pipeline.

They're then separated from the sediment and, if the project goes ahead, will be shipped onshore for processing.

There are broadly six environmental components being considered during the company's impact assessment phase, according to Dr Clarke.

There are sediment plumes on the sea floor, in the mid-water where the nodules are brought up the pipe, and again at the surface after the nodules are separated and the sediment is pumped out the back of the vessel.

And they're also looking at the risk of mobilising heavy metals in the sediment, disrupting potentially scientifically and medically useful genetic material, and impacting biodiversity. 

As for the number of undescribed species, Dr Clarke said he was surprised it was so low, and that there were far higher numbers of unclassified species on land often where terrestrial mining takes place.

"The global average [of undescribed species] is probably 90 per cent. I'm actually quite surprised that we've ... identified 10 per cent [of species in the CCZ] to be honest.

"As I said before, a lot of the nickel is coming from the likes of Indonesia which is incredibly diverse. In the likes of Indonesia, there are hundreds of thousands of species, many of which haven't been discovered. So you know you've got to be comparing apples with apples here."

He said that while there would be biota brought up with the nodules, the overall impact would be minimal, and that the company would focus on transparency.

"The definition of sustainable that we would use would be that we can take a part of this resource, but leave enough behind that we don't interrupt any ecological function — we don't disrupt carbon sequestration, we don't mobilise large amounts of toxins into the water column that are going to be bio-accumulated."

The company said it was adding interactive monitoring to its operations to try to address criticisms that the geographic isolation of deep-sea mining means it was free of public scrutiny. 

"We've gone out of our way to develop a system that makes us transparent," Dr Clarke said.

"There will be live feeds. There will be regular reporting back to the regulator. There will be observers onboard the vessel to observe what we're doing."

'Some weird cascade effect'

The CSIRO is leading several organisations to investigate the potential impact of The Metal Company's deep-sea mining proposal, and will make their findings public.

It's developing an ecosystem assessment plan that will "inform the company's environmental management plan and provide vital information for the [International Seabed Authority] to consider", according to a CSIRO article published late last year. 

The CSIRO said at the time that critical mineral supply was crucial for the green energy transition.

"We are not a proponent for deep-sea mining activity, that is simply not our role," said Dr Jeffrey Dambacher, a senior researcher with CSIRO's Ecological and Environmental Risk Assessment team.

"We're involved with the project because we want to provide a framework to assess the potential environmental impacts of deep-sea mining in a way that addresses the concerns of ISA, global stakeholders and The Metals Company."

The growing prospect of mining in the CCZ was part of the motivation for Ms Rabone's study.

She says knowing what is there is crucial for deciding if, where, and how any deep-sea mining should be done in the region.

"It's really important to do that baseline taxonomy, to find out what species are there, and that creates the bedrock for the next stage, which is then the ecology — what are the [species'] functional traits? Is there a role in the ecosystem where if they're mined, there'll be some weird cascade effect?"

Christine Erbe, a bioacoustics expert at Curtin University, researches how underwater sound impacts marine fauna.

She said there were too many unknowns at this stage to say whether deep-sea mining could be sustainable in the CCZ.

"We don't know much about the effects of noise on deep-sea species, and we don't even know much about what species live in these habitats," said Professor Erbe, who was not involved in the study.