Deep-sea mining: beyond the headlines
A decade ago I used to think deep-sea mining was a fairly straightforward issue. But I've come to realise how it is a complex topic, particularly in its wider context, which doesn't lend itself well to media soundbites.
It's the end of another annual meeting of the International Seabed Authority, and consequently a time when deep-sea mining is in the news again.
As my research investigates the ecology of some of the habitats being targeted for potential deep-sea mining (including work specifically to understand some of its likely impacts), I often get asked about it by news outlets.
Perhaps unsurprisingly, I think the reality of deep-sea mining lies somewhere between some of the investor-attracting promises of the industry, and the predictions of certain catastrophe by some NGOs.
So here's an attempt to set out the issues as I see them. It's a long article (about 8000 words, or ~25 minutes reading time), as there is a lot to consider for a full perspective. I don't apologise for that (it took me a lot longer to write than it will for you to read it), but I hope it is digestible.
Disclaimer
I don't receive, and have never received, any funding from mining companies - and nor do I receive, or have ever received, any funding from NGOs that are opposed to deep-sea mining (my research is publicly funded through grant proposals to the UK's science funding agency).
I have colleagues for whom each of those conditions apply - and in some cases both - and personally I don't think it affects the objectivity of their research at all. But just to be clear here for anyone who does get concerned about such things.
A further caveat: I will turn out to be wrong about some of the things here. In some cases, that's because the details span areas beyond my own particular field of research (though I have tried to include links to sources where relevant - and I will try to correct the text when I become aware of errors). But even within my field, I expect it too: finding out that your understanding of something is incorrect or incomplete is how science progresses. So I'm used to that - and this article is an attempt to summarise my current understanding.
What's at stake?
First of all, what's driving an interest in mining mineral resources on the ocean floor? It's not only capitalist greed, though undoubtedly those involved hope to become wealthier as a result.
We need more metals than we currently have for the "green transition": the replacement of our current energy infrastructure that produces greenhouse gas emissions (from burning oil, gas, coal etc) with zero-emission energy infrastructure based primarily on renewable sources (wind, solar etc).
That's not to say those metals have to come from the deep ocean - I'll come back to that - but first let's consider why we need the green transition.
Without that new energy infrastructure, we won't achieve the "net zero" goal that many countries have committed to reaching by 2050, to try to keep global warming as close to 1.5 degrees C as possible.
Right now we're at about 1.1 degrees C of global warming compared with pre-industrial times, and we're currently on course towards 2.7 degrees C of warming (i.e. hugely overshooting the 1.5-degree target).
Why have countries agreed a goal of trying to limit warming to 1.5 degrees C?
The impacts of 2 degrees C of warming, for example, are proportionally far greater than 1.5 degrees C. Hitting 2 degrees C rather than keeping to 1.5 degrees C would expose 420 million more people to extreme heatwaves, and expose 61 million more people in urban areas to severe droughts. And 2 degrees C of warming also causes much greater impacts on ecosystems and biodiversity, as conditions change in habitats, with knock-on effects for food production.
That's 2 degrees compared with 1.5 degrees (a 0.5 degree difference in warming) - and to reiterate, we're currently on course for 2.7 degrees of warming (i.e. another 0.7 degrees on top of that...).
In short, keeping global warming within 1.5 degrees C would prevent the deaths of several million people (the IPCC projects 250 000 excess deaths per year from climate change by 2050). And there's the further impact that has on global society, through migration of people trying to survive, and ensuing geopolitical turmoil. Plus the more severe global impacts on biodiversity - for example, shallow-water coral reefs that provide a home for perhaps a quarter of the species in the ocean are likely to be largely wiped out at 2 degrees C of warming, compared with 1.5 degrees C.
So that's what's at stake, and why we need more metals.
Which metals do we need - and how much of them?
Low-carbon or zero-emission technology depends on lots of different of metals: for example copper (for anything conducting electricity); lithium (for batteries); and some "Rare Earth Elements" (such as neodynium and dysprosium in magnets, needed for electric motors and wind turbines). Here's a 2022 list of "critical minerals" produced by the US Geological Survey, and here's a report on the need for some Rare Earth Elements in "green tech".
The need/demand for some elements may change as technology changes - for example, cobalt is currently used in most EV (electric vehicle) batteries, but the new types of EV batteries may use other elements than cobalt in future. But some remain in demand regardless (e.g. lithium is still required for those next-gen EV batteries, even if cobalt is not).
Let's take copper as just one example (as "humanity's first and most important future metal"): we need copper in the technology that generates electricity from renewable sources, and we need copper for the infrastructure that carries that electricity to where it is used, and we need copper in all the devices that use the electricity.
Offshore wind, for example, needs ~8 tonnes of copper per megawatt of generating capacity, in the turbines generating the power and the infrastructure delivering it to the grid ashore. Onshore wind needs ~2.9 tonnes per MW, and solar photovoltaics need ~2.8 tonnes per MW. Coal and natural gas power generation, in comparison, need ~1.1 tonnes of copper per MW of generating capacity.
To change all the internal-combustion-engine (ICE) vehicles currently on the UK's roads to battery electric vehicles (BEVs) requires ~2.3 million tonnes of copper (a typical ICE car contains ~23 kg of copper, while a similar-size BEV car contains ~53 kg of copper).
(Those data are from two recent research papers by Richard Herrington at the Natural History Museum, which are utterly recommended reading to understand this topic: "Mining our green future" [2021] and "The raw material challenge of creating a green economy" [2024] - and for any journalists wanting to understand the wider context of deep-sea mining for their audiences, Richard is definitely a good person to talk to).
As a result, the demand for copper (as one example) to achieve the "green transition" is huge. A recent report (May 2024) published by the International Energy Forum predicts that we will need as much copper in the next thirty years as we have mined in all of human history so far.
It's also worth noting that individual metals often aren't mined in isolation - many of them occur as "companion" metals. Cobalt is a good example - it occurs with copper, and with nickel, and so many "cobalt mines" are actually primarily copper or nickel mines, where cobalt is also being extracted as a companion metal. About 60 percent of the current global supply of cobalt comes from copper mines in the Democratic Republic of Congo.
Why can't we get the metals we need from recycling?
It would be great it we could just recycle the copper and other metals we're currently using to meet that demand, but unfortunately we can't. For copper, recycling can meet about 30 percent of current (not future) demand. There isn't enough currently in circulation, and we would have to wait for whatever is using the copper to come to the end of its operational life before it becomes available. And to hit net zero by 2050 and thereby try to limit warming to 1.5 degrees, we need to be building new energy infrastructure as quickly as possible.
We do need to improve the efficiency of recycling, but can't wait for that either. We're not too bad at recycling some metals: recycling of cobalt, for example, is already about 50 percent, with an expectation that recycling current-generation EV batteries from 2035 will boost that recycled supply even further. But current recycling of some other metals is very poor (for lithium, it's about 1 percent). The hope is that during a "dash for metals" to achieve the green transition, we also get better at recycling overall, so that recycling can then help to meet demand beyond the transition.
But recycling alone can't get us through the transition - and in the case of copper as an example, we need to mine more of it as a result.
Where do we want to mine?
Staying with copper as as example, the question then is: where do we want to mine the copper that we need for the green transition?
And this is where deep-sea mining becomes part of the discussion. There's copper in the "seafloor massive sulfide" deposits (aka "polymetallic sulfides") formed by hydrothermal vents, and there's copper in the "polymetallic nodules" (aka "manganese nodules") found on some abyssal plains.
There are other metals in those deep-sea deposits too, so the discussion is not just about copper. Polymetallic nodules also contain nickel, cobalt, and Rare Earth Elements that are needed for the green transition. And "ferromanganese crusts" - another type of deep-sea mineral deposit that forms on some seamounts - also contain cobalt, nickel and Rare Earth Elements.
So on one hand, the arguments of mining companies that we need metals found in deep-sea deposits for the green transition are correct (certainly for copper; though for some other metals, such as cobalt, future battery technology using other metals may reduce the need for some of them).
But on the other hand, the point made by NGOs that we don't necessarily need to mine the deep sea to meet the demand for those metals is also correct: we could meet the demand for copper and the other metals just through increased mining on land.
In the case of copper, the prediction that "we need as much copper between now and 2050 as we've mined so far in human history" perhaps sounds scary, but meeting that copper demand would involve the equivalent of opening one new large copper mine every year for the next 15 years (which is potentially feasible).
New mines on land don't just instantly spring into existence, however - the average time from discovery of a new copper deposit to mining it is around 23 years. But to get what we need to limit warming to 2 degrees C (not 1.5), we could potentially accelerate mining of all the currently known copper deposits on land.
But mining on land has impacts, of course, on biodiversity and on local communities. And the nature and extent of those impacts depends on where you mine. So we come back to that question: where do you want to mine?
Take Escondida, which is one of the world's largest copper mines, in the Atacama Desert of Chile (and contributes about 2.5 percent to Chile's GDP). That desert is home to some remarkable species of animals and plants of course, but it's not a hotspot for biodiversity like a rainforest, and desert life is pretty sparse, typically with widespread populations of species. There weren't existing local communities in the immediate vicinity of the mine, at altitude in the Atacama desert. And the power supplied for mining there is now 100 percent from renewable energy sources (primarily solar). So as copper mining goes, it has a lower environmental and social impact than mines in some other places.
In contrast, there's the Grasberg copper mine in the Indonesian province of West Papua, just upslope of the biodiversity hotspot of a rainforest (and next to the Lorentz National Park). Tailings disposal from the mine has impacted local waterways, and people have been killed in mine-related conflict and workforce protests.
Ideally, if possible, the equivalent of 15 additional copper mines that we need should be more like the Escondida mine in the Atacama Desert in terms of impact; and clearly we don't want 15 more mines like Grasberg.
But it might not be possible for all the additional mines we need to be like Escondida - the mines will be wherever the copper deposits are (and geopolitically it might not be desirable for them all to be under the jurisdiction of one country either).
We know where the copper is in the deep sea, so how would deep-sea mining compare in terms of impacts with mining in the Atacama Desert or mining in a rainforest?
That's the research question we're involved in answering, by investigating what the environmental and ecological impacts of deep-sea mining are likely to be.
A terrible choice
Before moving on to consider that research question, it's worth reiterating the overall context for deep-sea mining: our world faces a terrible choice.
We could resist further mining anywhere because of its impacts, but in doing so fail to curb higher levels of global warming, which will kill millions of people and have planet-wide impacts on habitats and biodiversity.
Or we can mine the additional metals needed for the green transition, which will inevitably result in impacts on some habitats, and possibly local communities, where that mining takes place - but avoid the global impacts of more severe climate heating.
We are now in a situation where there isn't a zero-impact option for the future. Thanks to the path that we (or rather our politicians) have followed in recent decades, we face that terrible choice. It's the kind of choice often used as a crux in stories (the "impossible choice", also known as "the hero's dilemma" - often framed as a "who do you save or sacrifice?" dramatic situation), and also the "trolley problem" in philosophy, but this is our reality, not fiction or a thought-experiment.
I hope you feel damn angry about us being in that situation - I certainly do.
The best we can do is try to choose the lowest impact forms of mining for the metals that we need, while getting better at recycling for the future (and try to fix our political systems that are structurally vulnerable to the influences of wealthy lobby groups, which contributed to getting us into this mess and continue to exacerbate it).
We therefore come back to the need to understand the impacts of the options we have for mining, to inform that terrible choice.
The research question
So the question that our research is answering is "what are the environmental and ecological impacts of deep-sea mining likely to be?" (and then the answer to that question can be compared with the impacts of the options for mining on land, to make an informed choice).
And I cannot emphasise this enough: we are doing the research because we do not yet know the answer to the question (not to find a particular answer).
If we already knew that deep-sea mining would be catastrophic, for example risking extinctions of species or disrupting the global carbon cycle in the deep ocean, we would be making that very clear to politicians and policymakers.
And if we already knew that deep-sea mining would be catastrophic, we wouldn't need a moratorium on the development of deep-sea mining for "further research" to understand its impacts; we could call for a ban on deep-sea mining right now, based on the evidence of our research, if that were the case.
It's possible that the answer to our research question could turn out to be that deep-sea mining poses a risk of species extinctions - in which case we could rule it out as an option to help provide the metals needed for the green transition.
But it's also possible that our research could find that the impacts of deep-sea mining might be similar to mining in the Atacama desert (we can't rule out that possibility, because we haven't completed the research) - in that case, deep-sea mining might end being considered as an option.
Note that neither of those are answers to the question "should we mine the deep sea?". They are answers to the question "what are the impacts of deep-sea mining likely to be?". Our research will answer that question, which will then need to be compared with the impacts of other forms of mining.
And it's not just the environmental and ecological impacts that need to be compared: there are also the social impacts, economic impacts, geopolitical impacts, and cultural impacts that need to be considered.
Those are the aspects that all need to be weighed up to answer the wider question "should we mine the deep sea?". As marine ecologists, we can only provide evidence on the aspect that is our area of research - and that's what we're doing - but that aspect alone doesn't necessarily provide an answer to the wider question.
What ecological impacts could rule out deep-sea mining as an option?
This is a question that the International Seabed Authority continues to grapple with. Its documents talk about the need to avoid "serious harm" to the marine environment - but exactly what "serious harm" means is harder to establish (as illustrated in the quote at the end of this interview with the new Secretary-General of the ISA, Leticia Carvalho: "What is the definition of harm? That's what we have to discuss").
We can take a pragmatic approach, however. Separate from the International Seabed Authority, the United Nations has brokered an international agreement - the Convention on Biological Diversity - to protect biodiversity. So as an absolute minimum, any regulation of deep-sea mining should seek to avoid the risk of reducing biodiversity - in other words, sending any species extinct.
Note that is only a minimum to avoid - but if deep-sea mining cannot be conducted without risk of species extinction, then it should be a non-starter, given the UN Convention on Biological Diversity.
So for now, let's take that as a definition of "serious harm", and look at what we know so far - and what further research will be required - to understand risks of species extinction from deep-sea mining.
There's more than one type of deep-sea mining
Deep-sea mining is not "one thing": there are different types of deep-sea mining being considered, targeting different deep-sea habitats, and those habitats differ in their vulnerability when it comes to considering any potential risk of species extinction.
It really annoys me when a media article about deep-sea mining highlights some of the species that thrive around hydrothermal vents, and then goes straight to discussing the prospect of mining manganese nodules on abyssal plains. That's the same as talking about species that are only found in the Galapagos Islands, and then talking about the prospect of mining in the desert of Western Australia.
The deep sea is not a single habitat: it encompasses lots of different environments, just as "the land" does, and each has its own ecological patterns and dynamics, which make some more vulnerable to mining disturbances than others.
(Life at a deep-sea hydrothermal vent; NERC ChEsSo Consortium)
Understanding risk of species extinction from deep-sea mining
There is one type of deep-sea mining that already know would risk species extinctions: mining at active hydrothermal vents for the copper-rich "seafloor massive sulfide" deposits that they create.
Biologists, like me, who study the ecology of those habitats have been unanimous in telling policymakers that active hydrothermal vents would be vulnerable to species extinctions from deep-sea mining.
The total global area of active hydrothermal vent habitat is around 50 km2 (less than half the size of Disney World in Florida), and that habitat is home to more than 400 species of animals that are not found in any other habitat on our planet.
If you were mining on land and said you wanted to mine an area of 50 km2 that was home to more than 400 species not found anywhere else on Earth, it would be a complete non-starter under any responsible regulatory regime.
The actual risk to biodiversity in vent habitats is from cumulative impact at a regional level, reducing "mature" vent habitat that some species might require in those successional ecological systems (and I wrote an explainer about it a decade ago, available here).
Mining at active deep-sea hydrothermal vents is incompatible with international commitments to protect biodiversity. No further research is needed to understand that, and I hope we have been clear about it.
The International Seabed Authority has yet to produce the rules for mining of seafloor massive sulfides, and when they do, I expect those rules to protect active hydrothermal vent habitats from deep-sea mining (and frankly, if the ISA doesn't do that, I think it would risk losing the trust of the scientific community).
But if we already knew that other forms of deep-sea mining - in particular, manganese nodules - would similarly risk species extinctions, we would be as clear about it as we have for active hydrothermal vents.
What about nodule mining?
So how does nodule mining differ, as a prospect, from mining sulfides at hydrothermal vents?
For starters, there's the scale of the habitat involved. Manganese nodules form on some of the world's abyssal plains, which are a huge habitat globally (covering more than a quarter of the ocean floor, though not all abyssal plains have manganese nodules on them).
The area of particular interest for nodule mining in the eastern Pacific is called the "Clarion-Clipperton Zone" (often abbreviated to CCZ), which covers about 6 million km2 of seafloor stretching from offshore of Mexico out to south of Hawai'i.
Within that area, about 1.5 million km2 of the seafloor has manganese nodules in sufficient abundance to be of interest for mining - and that 1.5 million km2 is 30 000 times larger than all the world's active hydrothermal vents.
So that makes nodule mining a different prospect to mining at vents - it is not targeting a globally rare habitat.
In some ways, the 1.5 million km2 of seafloor being targeted in the Clarion-Clipperton Zone is a huge area (just over six times the area of the UK). But from another perspective, it is 0.5 percent (i.e. half of one percent) of the global deep ocean (and about 0.3 percent - less than one-third of one percent - of the surface of our planet).
And the projections are that around 30 percent of the 1.5 million km2 area would be actually mined in the next 20-30 years if mining went ahead there. The other areas within it are either unsuitable seafloor terrain for mining (dotted with "abyssal hills" - our planet's most abundant surface feature) or will be required to become "Preservation Reference Zones" (PRZs) for monitoring mining impacts.
So the prospect is for around 450 000 km2 to be involved in actual mining, i.e. around 0.13 percent (i.e. just over one-tenth of one percent) of the deep ocean.
That's not to belittle the scale of the proposition at all - that 450 000 km2 is still a huge area to expose to an industrial activity (just under twice the size of the UK), and the extent to which impacts spread beyond that area is a topic of further research. But when someone claims that mining there will somehow wreck the entire global ecosystem of the deep ocean - all 305 million km2 of it - you can perhaps see how that is likely to be nonsense.
Understanding risks of species extinction in nodule mining
For the purposes of assessing risks of species extinction in nodule mining, let's assume a worst case scenario that whatever lives at the seafloor will be wiped out in areas that are mined (rather than a few animals potentially surviving in gaps between mining machine tracks etc).
First of all, let's consider what lives on the seafloor of the area of interest in the Clarion-Clipperton Zone. And the short answer - and I think it's important to be honest about this - is "not very much" (very different from the abundant life at hydrothermal vents).
The seafloor in the area of interest is 4000 to 6000 metres deep, and the surface ocean above has very little algae growing in it, because it's in an area of the ocean where there are relatively few nutrients. So there's very little food sinking from above onto the ocean floor - and consequently not much life down there, compared with other habitats in the deep ocean (or elsewhere on Earth).
If you were to collect everything living on and in a square metre of the seafloor there, and weigh it all together, it would be tiny compared with the "biomass" from doing the same for a square meter of a coral reef, or a seamount, or around a hydrothermal vent - or even the ground in a local park, for example. The seafloor of the CCZ is one of the least inhabited places on our planet.
But although the biomass there is low, the biodiversity (number of different species) is relatively high (much higher than at hydrothermal vents, for example). There are an estimated 6000 to 8000 species of animals living on the seafloor in the Clarion-Clipperton Zone - and that estimate is based on the rate at which we are finding new ones, as so far only a few hundred have been identified as known species or described as new ones.
Some of those species are undoubtedly beautiful, such as "gummy squirrels" and "Barbie pigs", which are colourful popular names given to some of the types of sea cucumbers found in the CCZ. Perhaps because they're new to us, and because they're from the mysterious ocean depths, we can appreciate how weird and wonderful they seem. But if we were to find a dandelion for the first time in the deep ocean, I think we'd regard it as equally weird and wonderful - but familiarity perhaps blinds us to the wonder of nature when it's closer to home.
So we have a situation in the CCZ where there are lots of species, but members of each species are few and far between - and their sparse populations are often spread over a very large area (again, unlike hydrothermal vents, where abundant populations are crammed into tiny island-like habitats).
The sponge Plenaster craigi is an example: it's typically a few millimetres in size, and was described as a new species in 2017. It's one of the most abundant animals found on the manganese nodules themselves, and we already know that its population is spread over at least 900 km of seafloor in the CCZ.
When it comes to assessing potential risk of species extinction from nodule mining, what matters is the distribution of a species in comparison with the area being mined.
The ISA has already established large "Areas of Potential Environment Interest" (aka "APEIs") that are effectively marine reserves: thay have been designated as areas of the CCZ that will never be mined. There were originally nine APEIs, increased to thirteen in 2021, and together they cover 1.97 million km2 of seafloor (an area more than eight times the size of the UK).
If they contain the same species as the area being targeted for mining, and are not dependent on the populations in the mining area, then they should protect species from any extinction risk arising from mining impacts.
That "if" is one of the big questions: the current APEIs are largely spread around the edge of the CCZ, while the mining claim areas are in its centre. So an important part of research is assessing how representative they are as potential reserves for marine life in the area - and whether they are in the right place.
An analogy closer to home
As an analogy, understanding the potential risk of species extinction from nodule mining it comes down to whether we're dealing with the equivalent of dandelions or great-crested newts.
Whenever we mine or build on land, we don't worry about any risk of sending dandelions extinct. We know that the population of dandelions spans a much larger area than our disturbance of their habitat, and that dandelions are great at dispersing their seeds on the wind, and also great at growing on any speck of bare earth habitat remaining among whatever we're doing.
But if we were planning a development on land that affected the few ponds with particular conditions that provide a habitat for great-crested newts, and thereby threatened to wipe out the population of that species, that would be a non-starter for regulatory approval (in the UK, risk to great-crested newts is enough to halt development even in the garden of a former Prime Minister).
Some of the species living on the seafloor will be like dandelions (possibly Plenaster craigi among them, based on research so far). But some of the species in the CCZ could turn out to be like great-crested newts, with restricted habitats that might not be protected by reserve areas.
The "further research" we are doing therefore includes investigating the distributions of species populations across the CCZ, between potential mining areas and protected areas, and assessing how good species are at dispersing as larvae (the equivalent of dandelion seeds for underwater animals).
So far, there are no obvious "red flags" in that regard. Again, nodule mining contrasts with vent mining here: more than 60 species of animals living at vents have been listed as "endangered" by potential deep-sea mining on the IUCN "Red List" of threatened species. But no species from the CCZ have yet been added to the Red List as threatened by nodule mining.
We've barely begun assessing the risk from nodule mining for each species in the CCZ, however. And there are 6000+ of them - if each one needs to be checked in that way for potential risk of species extinction, then that "further research" is probably going to take a long time...
How long will the seafloor take to recover from nodule mining?
In the 1980s, a German research programme (DISCOL - DISturbance and reCOLonisation) began investigating the potential impacts of deep-sea mining by conducting an experiment in the Peru Basin (rather than the Clarion-Clipperton Zone), where they scraped the seafloor with a plough-like device to simulate the tracks of a mining vehicle.
Return visits to those experimental scars over 26 years revealed little signs of recovery (recolonisation of the disturbed areas by the marine life usually found on the seafloor there) over that timescale. This has led, quite understandably, to concern about how long the seafloor will take to recover from nodule mining - and whether the abyssal plain seafloor is particularly vulnerable and slow in that regard.
That's another area of ongoing research (watch this space...).
Often when a disturbance alters the topography of a habitat, it changes the conditions of that habitat, resulting in lasting changes to what lives there. In my local woods, for example, there's a pond that is actually a bomb crater from the Second World War, more than 80 years ago. What lives in it - now that it's a depression filled with water - is very different to what lived there before and what lives in the surrounding woodland. If we were surveying that feature on the ocean floor, we would conclude that there has been very little recovery of the species populations previously living in that disturbed area, after more than 80 years.
Mining machine tracks create depressions in the seafloor that can fill with finer sediments than surrounding areas, which can favour different species. So further research is underway to understand those patterns and processes, and their consequences.
Nodules themselves form very slowly, typically over millions of years. So mining certainly will have lasting impact where nodules are removed - the hard surfaces that they provide on the otherwise fine mud of the abyssal plain will not regenerate on any human timescale. And some types of marine life favour those hard surfaces, so that reduces habitat for such species.
But again, what will matter for determining any extinction risk is how widespread the populations of those species are, compared with the areas being mined and the areas set aside as reserves.
What about other environmental impacts from nodule mining?
So far we've just considered the direct impact of mining machines killing animals in their path, but there are other impacts to consider from mining operations.
The mining machines also stir up seafloor sediments as they trundle along. Those sediments - like a dust cloud - then settle on the surrounding seafloor. One potential impact is whether they might smother animals alongside the paths of the mining machines. Research already shows that these seafloor sediment plumes don't spread out over as wide an area as some people originally imagined, so we at least now understand that it is a local impact (undetectable beyond a couple of kilometres from a mining track). But which animals cope with it - or indeed benefit from it, with some species colonising newly sedimented areas better than others - is an area of ongoing research.
In the context of understanding risk of species extinction, however, this additional impact doesn't change anything - what matters is how widespread the population of a species is compared with the impacted area.
Most proposed nodule mining operations also involve a "mid-water plume" of sediments. Nodules collected by the machines on the seafloor are piped to a surface ship above, where the nodules are removed, and the remaining sediments are discharged down another pipe, released into the ocean at perhaps 1500 metres deep (to disperse high above the seafloor). That mid-water plume also has impacts - not on life on the seabed, but on what lives in the interior of the ocean at those depths.
Research is therefore investigating how far that mid-water plume disperses, what the conditions are inside the plume, and how that could affect mid-water life. For example, many mid-water animals use bioluminescence to hunt for prey and attract mates - if water is sufficiently turbid in the mid-water plume, it might cut down the range over which those bioluminescent signals work. And lots of sediment could even clog up some animals such as deep-sea jellyfish.
But again, when it comes to risk of species extinction, what matters is how widespread the populations of any affected species are, compared with the impacted area.
Potential impacts on fisheries are one of the social considerations involved in nodule mining, if the mid-water plumes impact any commercially fished species. The CCZ is not a prime area for fisheries, however, because there is so little algal growth providing food in the surface ocean there - but any impacts do need to be considered. And some migratory species that are fished elsewhere pass through the area, so the impacts on them from the mid-water plumes need to be assessed too.
There is also underwater noise involved in mining operations, and its impacts need to be considered too. But the noise is at a lower level than some other industrial activities in the ocean (particularly seismic surveying for offshore oil and gas), for which ways of regulating the activity already exist (e.g. with independent marine mammal observers aboard vessels, who can halt operations when whales are sighted nearby) that could similarly be used in nodule mining.
An "Impossible" solution?
There is one approach for nodule mining being developed that potentially avoids several of these further environmental impacts. A company called Impossible Metals is developing harvesting machines that hover above the seafloor, rather than trundling across it on tracks, and pick up individual nodules with robotic arms, guided by cameras and AI (technology adapted from the fruit-picking industry). Once the machine's payload is full with picked nodules, it rises back to the surface ship (rather than pumping nodules up a pipe with a slurry of sediment), so there is no mid-water plume discharge.
By picking individual nodules rather than scraping them up, the Impossible Metals machines don't generate the same seafloor sediment plume either. And they can be programmed to avoid picking up nodules with obvious marine life on them, and to leave a certain percentage of nodules behind on the seafloor as habitat along their path, rather than removing everything.
Inevitably, the Impossible Metals machines are smaller in scale than the traditional machines developed by other deep-sea mining companies, but lots of them could be deployed from a vessel (instead of one large machine attached to the ship by the riser pipe).
The company has tested prototypes in shallower waters, and is planning deep-sea tests in the CCZ. Their starting-point was the list of concerns raised by scientists about mining impacts - and their design goal is to engineer a way around them, potentially enabling collection of nodules without those impacts. If they are successful, it will be interesting to see if the regulator (the ISA) might make that technology the requirement for the industry (and whether NGOs would accept that outcome, if it enables low-impact nodule mining).
What about impacts on "ecosystem services"?
One of the "ecosystem services" (things that nature does that benefit us) that the deep ocean provides, as often mentioned in the context of protecting it from deep-sea mining, is carbon sequestration.
When algae bloom in the sunlit waters of the upper ocean, they use up carbon dioxide from the atmosphere to grow. If their remains sink into the deep ocean (without being eaten and turned back into carbon dioxide by the metabolism of whatever eats them), and if those remains eventually get buried on the ocean floor (rather than being eaten by what lives there, and turned back into carbon dioxide by their metabolism), then that removes carbon from the atmosphere.
There are a lot of "ifs" in that process, and consequently only a fraction of the carbon absorbed from the atmosphere by algae at the surface of the ocean ends up buried in the sediments of the seafloor. But overall, this "biological carbon pump" is important in drawing down carbon dioxide from the atmosphere, and locking some of it away on longer timescales, thereby helping to regulate climate.
Some of the more extreme statements of NGOs have implied that deep-sea mining could disrupt this process on a global scale. But the area where nodule mining is being contemplated, in the Clarion-Clipperton Zone of the eastern Pacific, happens to be a part of the world where the "biological carbon pump" of the ocean is particularly weak.
There's not much algae growing in the surface waters of the ocean there, largely because of a lack of nutrients in that region. As a result, the natural rate of sedimentation reaching the ocean floor - as "marine snow" - is among the lowest in the world. Very little carbon gets buried in seafloor sediments there over time, which is also one of the reasons why manganese nodules are abundant there. The nodules form very slowly from chemical reactions on the seafloor, often growing around objects such as fossil shark teeth (in some cases, fossil Megalodon teeth that are at least 2.3 million years old). In the CCZ, they don't get buried in that time by sediments falling from above, unlike in other areas.
So even if nodule mining reduced the burial of carbon there, its global impact would be tiny: the area of CCZ being targeted by mining is half of one percent of the global deep ocean, and an area where there is relatively little natural carbon sequestration.
And it's not clear how deep-sea mining would actually disrupt carbon sequestration. If discharge plumes reduce mid-water life, that could perhaps reduce the rate that carbon sinks to the ocean floor: although some carbon dioxide is released when animals eat and use food, some undigested food gets packaged into poop that can sink more swiftly to the seafloor. So fewer mid-water animals might mean less poop, and thereby reduce that rate of carbon flow down through the ocean.
But fewer animals in mid-water also means less chance of sinking carbon being eaten, and some of it turned back into carbon dioxide, during its descent. So even if it sinks more slowly with less mid-water life, perhaps more of it would reach the seabed - it's hard to guess the consequences.
And a decrease in life on the ocean floor itself, as a result of mortality there from mining, could potentially increase the burial of carbon there, if there's less life to eat it when it settles and thereby turn it back into carbon dioxide.
Further research is required, but given the small proportion of the ocean affected, and the low rate of natural carbon sequestration there, it's not a priority for concern - it's unlikely to have an impact on that process in the deep ocean at a global scale. And NGOs citing "carbon sequestration" as a reason to protect the deep ocean from mining should perhaps be careful what they wish for: from a purely numerical perspective, if deep-sea mining reduces life on the ocean floor, that could perhaps seem to be "good" for carbon sequestration.
Recently colleagues have uncovered a possibly unrealised "ecosystem service" from manganese nodules: they may also produce oxygen at the ocean floor, through a process of electrolysis. This "dark oxygen" might be locally important for marine life, particularly as the deep ocean becomes deoxygenated as a result of climate heating. Further research is needed to check the evidence for that discovery, and if it is confirmed, to understand how important that process could be for supporting deep-sea life in the region (and its effects are likely to be local, given the relative small size of the global deep ocean involved).
If the generation of "dark oxygen" turns out to be a significant for deep-sea life in the region, there are already ways of potentially managing the impacts of mining on that process. On land, there are "natural capital" approaches, where developments that affect ecosystem services are offset by protection or creation of areas providing the same services. The "APEI" areas of the CCZ that are protected from mining, and "Preservation Reference Zones" required in mining areas, offer a possible way to provide that kind of spatial management for nodule mining.
How does deep-sea mining compare with impacts of other human activities in the deep ocean?
This is not "whataboutery", but an attempt to put the potential impacts of deep-sea mining, which seem to grab public and media imagination, into context.
Industrial deep-sea mining has not yet begun. But we are already inflicting impacts on the ecology of the deep ocean, at a global scale, that far outstrip the worst case scenarios of impacts from deep-sea mining.
These impacts from other human activities are not a reason to ignore the potential effects of deep-sea mining (and it's certainly not a choice between "mine the deep ocean" or "suffer climate heating"). In fact, other impacts on the deep ocean provide an argument to avoid adding further stress to its ecosystems where possible, on top of the damage that we are already causing. But they also underline the urgent need to do the hard work of curbing greenhouse gas emissions as quickly as possible.
Climate heating affects the deep ocean in several different ways - and its impacts are felt not just in the half-a-percent of the deep ocean represented by the mining area in the Clarion-Clipperton Zone, but worldwide, in all regions and across all deep-sea habitats and species.
Our greenhouse gas emissions trap more heat in the atmosphere, but that extra heat doesn't stay there. More than 90 percent of it is absorbed by the ocean - and so is some of the carbon dioxide that we add to the atmosphere from burning fossil fuels. That uptake by the ocean then has several effects:
(1) the ocean is warming, and that includes the deep ocean. By 2100, seawater temperatures at 3000 to 6000 metres deep are set to increase by an average of 1 degree C - and as it's usually pretty chilly (typically about 2 degrees C) at those depths, that change is fairly dramatic for what lives there;
(2) deep ocean waters are becoming less alkaline ("ocean acidification"), which changes what lives where; animals with calcium carbonate skeletons, such as deep-water corals, may be more restricted in the depths at which they can live as a result;
(3) less food is sinking into the deep ocean from surface waters - and the biomass of mid-water life in some regions may reduce by 22 percent by 2100;
(4) the overall amount of oxygen in the ocean, on which all animal life depends, has declined by 2 percent during 1960 to 2010, and is set to decline much further.
That last impact - "ocean deoxygenation" - is one that particularly worries me. It's the result of a triple-whammy of effects: firstly, less oxygen dissolves in warmer water, so the now-warmer ocean contains less oxygen. But on top of that, organisms respire at a greater rate at higher temperatures, using up that oxygen even more quickly. And thirdly, ocean warming is weakening the deep-ocean currents that sink from polar regions through the ocean depths, carrying oxygen from the atmosphere to all the life down there.
That ocean circulation takes centuries to complete its journey, and the weakening that has already happened means that by the year 2400, the deep ocean will end up with 10 percent less oxygen overall than it had in pre-industrial times. That change is already "baked in" from the climate change that has happened so far - it will just take a while to spread through the deep ocean. Every day that we delay from achieving "net zero" in emissions simply makes that impact even worse. And it is a global impact on deep-sea life.
It will change the distributions and fate of species throughout the deep ocean. As some regions will be affected more than others, some species will be forced into new regions, impacting the populations of other species that become their prey or competitors. And some species might expand their distributions - vampire squid, for example, seem well-adapted to low-oxygen conditions - while others could be threatened if they cannot adapt.
Widespread changes in the patterns of deep ocean life are therefore coming as a result of ocean deoxygenation, while we're still trying to understand existing patterns so that we can inform the management of other human activities.
There are also impacts on the deep ocean from litter (including microplastics in the guts of animals in ocean trenches) and pollution (including from accidents in offshore oil and gas operations), and from deep-water fisheries (including the destruction of vulnerable habitats such as deep-water coral mounds and sponge gardens from bottom-trawling), and they are also important. But for context, they are not as widespread in terms of species and habitats affected as the global impacts of climate change in the deep ocean.
I'm encouraged that concern over deep-sea mining prompts people to be interested in and care about the ecology of the deep ocean. I hope that can be extended into concern about the impacts we're already having on that ecology, which are even more widespread than those from mining could be, and the choices we face to do something about them.
Where are we now?
To recap:
(1) We don't yet fully understand what the environmental impacts of deep-sea mining would be (particularly for nodule mining), which is why "further research" is needed.
(2) We don't yet know how those impacts will compare with other forms of mining needed for the green transition.
(3) We also don't yet know how other impacts beyond environmental - social, economic, cultural, geopolitical - will compare either.
Together, those provide reasons for a precautionary pause at the moment, rather than rushing ahead with it.
At the of writing, 32 countries including the UK have called for a moratorium on deep-sea mining to allow further research to understand its impacts. That's almost 20 percent of the nations who are parties to the UN Convention on the Law of the Sea, and thereby represented at the International Seabed Authority.
A moratorium is a pause, not a ban, but in the regulation of some other human activities in the ocean, a moratorium has led to a ban.
In 1983, for example, countries agreed an international moratorium on the dumping of low-level radioactive waste in the ocean, pending further research into its risks and impacts. Subsequently, a total ban on ocean dumping of all types of radioactive waste came into force in 1994.
Will people actually accept the findings of "further research" on its impacts?
The question I have, as a scientist undertaking the "further research" that has been called for on deep-sea mining, is whether all those calling for a moratorium will accept whatever the results of that research turn out to be.
What if, when we have our answers, the environmental impacts of nodule mining turn out to be similar (or better) than the lower-impact mining in the Atacama Desert, and certainly better than high-impact mining in a rainforest? And what if the overall social impacts are lower than terrestrial mining?
If that's what the results of further research show when they are put into context, then some forms of deep-sea mining could (and arguably should) end up being considered as part of the mix for getting the resources that are urgently needed for the low-carbon transition.
But I suspect some of those currently calling for a moratorium might not accept that outcome.
So if you're currently opposed to deep-sea mining, and actually don't ever want to see it go ahead, then please don't call for a moratorium. Please have the courage and honesty to call for a ban, on principle, right now. And state the principle, so that it can be clearly represented as a position in the debate.
For some, the principle of subjecting the ocean to another form of industrial activity, when there are alternatives for meeting the demand for metals, is enough to be opposed to deep-sea mining. But in that case, figuring out the details of what the impacts are likely to be doesn't really matter.
France is one country so far that is calling for a ban on deep-sea mining, rather than a moratorium to allow further research.
Principled opposition to deep-sea mining
There are plenty of possible reasons to be opposed to deep-sea mining on principle, with no further research required on environmental impacts.
For example, when deep-sea mining was first mooted at the United Nations in 1967 by Malta's ambassador Arvid Pardo, the proposition was that the then-seemingly-inexhaustible wealth of the ocean floor (which the UN went on to define as the "common heritage of mankind", as it lies beyond the boundaries of national jurisdictions) could be used to address past injustices, to help lift some countries out of poverty through industrial development and create a more equitable global society of nations.
It's also worth noting that during the 1970s, several consortia of companies carried out successful test mining of manganese nodules in the CCZ (you can browse the history in my timeline here). Deep-sea mining was poised to begin in areas beyond boundaries of national jurisdiction, with no regulatory or benefit-sharing system in place. The final negotiations of the UN Convention on the Law of the Sea, and subsequent creation of the International Seabed Authority, prevented that possible "wild west" situation - and provided what has essentially been a moratorium for the past four decades.
But by the time the way that the "common heritage" benefits could be delivered was agreed in the early 1980s, when the UN Convention on the Law of the Sea was finalised and signed, some of the details had become quite different from Pardo's original vision.
The International Seabed Authority, which is tasked with delivering the "common heritage" benefits from deep-sea mining, has no capacity of its own to extract minerals from the seafloor. So it has made plans, on paper at least, to create a commercial arm known as "the Enterprise", which will enter into contracts with mining companies to deliver the "common heritage" benefits for humanity.
In practice, that means a partnership contract with mining companies for further mining. The profits that the ISA receives can then be used for "common heritage" investments (or possibly even the raw materials from that further mining, which could be directed to developing nations to stimulate their "green-tech" sector growth).
But the mining companies involved in partnerships with "the Enterprise" won't be working pro bono. They will also receive profits from that arrangement for further mining to realise those "common heritage" benefits.
So under the ISA's plans, mining companies stand to gain twice: once as contractors, profiting from mining their own licence claim areas - and potentially again as partners for "the Enterprise", sharing in the profits of an activity that is intended to deliver the "common heritage" benefits to all humanity.
Each dollar that ends up becoming available to provide a "common heritage" benefit is likely to be matched by at least another dollar going to a mining company (partnerships between mining companies and governments are usually at least 50-50 in the mining company's favour, so we should expect the same for partnerships with "the Enterprise" of the ISA), on top of the company's income from working up their own licence claims.
And while the common heritage dollars trickle down to provide benefits shared among the billions of people on our planet, the few already very wealthy shareholders of mining companies stand to gain proportionally much more from that arrangement. Of course, they are the investors who are risking their own money in a nascent industry. But overall, the "common heritage" deep-sea mining as currently envisioned by the ISA in my opinion looks likely to widen the gap between rich and poor, not reduce it.
That's the opposite outcome of Arvid Pardo's admittedly 1960s utopian vision of how deep-sea mining could benefit humanity. And by the signing of UNCLOS in the early 1980s, Pardo himself had become disillusioned by the direction that had been decided for it. In a Washington Post article in 1981, he described the proposed public mining company (now "the Enterprise") as "stupid".
There are more sophisticated legal instruments now available to define and realise "common heritage" benefits of deep-sea resources, including "rights of nature" approaches in law and recognising the value of preserving deep-sea biodiversity so that we can learn from the ingenuity of nature in its genetic resources. But the ISA seems still to be largely progressing along train-tracks laid down 30 years ago when it was founded, regarding financial income as primarily the way to realise "common heritage" benefits, and hoping to use that to address structural problems in global society.
For me, the approach of "the Enterprise" is reason enough to have some reservations about deep-sea mining developing along the lines that the International Seabed Authority has set out. And those reservations have nothing to do with environmental impacts.
Personal view
The research in which I am involved will show what the ecological impacts of deep-sea mining are likely to be - for good or for ill - and those results will be checked by other scientists not involved in the work (in case any personal reservations colour the objectivity of our work as scientists).
So for what's it's worth, my current view personally is:
- I think a pause to enable further research into the impacts of deep-sea mining is sensible (while acknowledging that there is an urgent need for more metals to enable the green transition, with millions of lives and impacts on biodiversity far greater than worst-case scenarios of deep-sea mining at stake if we fail in that goal; so if we do pause on deep-sea mining because of current uncertainties, we absolutely must make urgent progress reducing emissions wherever possible in the meantime);
- we already know that mining of active hydrothermal vents would risk species extinction, and therefore deep-sea mining targeting those particular habitats should be ruled out;
- we can't rule out nodule mining on the basis of environmental impacts, because we haven't yet completed the further research into the impacts of that form of deep-sea mining;
- nodule mining could potentially turn out to be lower in overall impact - environmentally and socially - than some forms of mining on land;
- but I have some reservations about the ISA's development of deep-sea mining, based on other principles that are separate from environmental impacts.
Moratorium vs ban?
For those who feel deep-sea mining is "just wrong": please ask yourself why you feel that way.
We have a cultural tradition of populating the deep sea with monsters of our imagination. Hell is "down" in many mythologies, and "monsters of the deep" have been a popular trope through history, from the medieval Kraken to recent Hollywood movies such as "Underwater" (and even in science, our terminology evokes a dark underworld, for example with "abyssal" plains and the "hadal zone" of ocean trenches).
Has deep-sea mining, when framed as certain to cause global environmental catastrophe, perhaps become a modern deep-sea monster of our imagination? One where the monster is "us" - or rather, representing the destruction of nature by human greed - and opposing that monster can be a way of expressing our personal values and identity.
Remember that we don't have actual evidence, at this stage, that the impacts of deep-sea mining will be catastrophic (that's why "further research" is being called for).
When research clarifies what the impacts will actually be - and how they compare with other forms of mining - perhaps we'll see a different picture than the one we imagine.
(2020 movie "Underwater")
But if you can't imagine ever accepting deep-sea mining being an option to help achieve the green transition, regardless of whatever further research finds out about its impacts, then please consider your reason for that view.
I seldom see the question "would you ever consider accepting deep-sea mining as an option, depending on what further research finds?" put to NGOs that campaign against deep-sea mining by supporting a moratorium for further research - and for clarity I would like to know their answer.
And when a spokesperson in a media interview states that deep-sea mining would certainly be catastrophic: journalists, please ask them to provide the peer-reviewed research paper, based on observational data, that contains the evidence for that statement. Because if that evidence already existed, we wouldn't need a moratorium to enable further research.
Thank you for reading if you made it this far!
Jon Copley, August 2024
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