The key thing you are trying to achieve is fixing carbon. That is net conversion a kg of atmospheric carbon into two kg (dry wt) of biomass, which sinks to the bottom.
The four biggest components of biomass are C, H, O and N. Water provides the H and O, and CO2 provides the carbon. For cyanobacteria, atmospheric nitrogen provides the N. For other phytoplankton, nitrate that leaks out of the cyanobacterial provides the N.
But biomass also contains other components, P, S, Mg, Fe, Co, and a bunch of other minerals, which they need to get in their diet, just as we do. Phytoplanton contains a lot of diatoms, so silica is also a nutrient (but this may simply be because hydrovents contain a lot of silica, so you get a lot of diatoms). We are talking a natural process--we aren't in a bioreactor, where we have better control over things--so things are going to be complicated.
SO for every ton of carbon you sequester you will need to provide some of these other nutrients, Phosphorous likely, and certainly iron. Perhaps others. You can figure you will need about 1 kg of phosphorous for every 50-100 kg of carbon you sequester. There's plenty of sulfur in seawater so that's not problem.
Thank you for this post. Fascinating and new to me, although I've been paying some attention to carbon removal technology since I wrote an article (and then a short book) about direct air capture of CO2 for FORTUNE magazine in 2011. I'm sure you know that there was a startup company called Planktos that intended to make a business out of ocean iron fertilization at about that time. I hope that in a future post you will write about (1) the costs of this technology and (2) the business model, if any, for bringing it to scale and (3) the politics. Surely there will be opposition from environmentalists but by now I hope that the more mainstream green groups recognize the need for CDR.
But of course it's impossible to know how much this is really going to cost until you go and do it. Cost discovery is the far end of a process of learning-by-doing and economies of scale.
For now all we can really say is that the *materials* to do this cost almost nothing (pennies per ton of CO2 in an iron-only scenario, less than $5 per ton in an iron+phosphates scenario). But of course the materials aren't really the point, it's the deployment and the monitoring, reporting and verification that cost money. How much? Your guess is as good as mine.
The business model and the politics are deep waters, too. I spend all my time thinking about this stuff. More to come for sure.
I believe there are desert areas below sea level. I remember reading about such a place in Mexico. I was thinking you could pump in ocean water to create a large salt water lake. You could experiment with these proposals there. If it worked the lake could absorb a lot of co2 without affecting the ocean ecosystem.
Yes!! The biggest one is in Egypt — a dried up former sea known as the Qattara Depression. I talked to some guys working on this. They want to dig a ditch from the Mediterranean to bring water over, with a big hydro-electric dam in the middle. It's pretty cool. An added plus is that the evaporation from the project should increase rainfall just east of it, across the Sinai and into Arabia, which are all places that could use more rain.
There was an example in the interior of Australia. Many decades ago some entrepreneurs started a project to pipe sea water to a below sea level area of desert in an effort to build an inland sea and even engineer more rainfall on the continent. The project was halted as it caused salt increases in groundwater that ruined grazing land and because the corrosive effect of salt and its depositions made maintaining the canals too expensive.
Is the only proposed human intervention adding iron to LNLC regions? Or are other steps necessary, like modifying trichodesmium cultivars for survival in LNLC habitats?
Edit: upon further reading, the implication seems to be that the only thing the hydrothermal vents added the example was iron. I think it could be said clearer though that there are LNLC areas, that shallow hydrothermal vents add just iron, leaving areas high in iron but low in nitrates and phosphates, and that results in trichodesmium blooms, and that this might extend to LNLC iron fertilization in general. It would be useful to have a clear takeaway message of “iron fertilization in HNLC areas may have problems, but these are probably solved by just fertilizing LNLC areas instead”.
I mean, it's such early days. The researchers I talk to tend to think trichodesmium are hardy old buggers and don't need any genetic messing-with to thrive, just nutrients. But who knows where that debate will be 10-20 years from now.
The research on those shallow vents seems to find that iron is the main thing making a difference, but again this needs farther study. Of course a natural process like a vent isn't going to be releasing a controlled flow of pure minerals, and there's certainly other stuff mixed in with the iron, and probably some phosphates too. I know it feels like a cop out when scientists say "we need another study" but in this case...man, we really do need more study.
Ok, yes, I didn't know about this version of carbon capture. In your effort to tell a good story though you left out some important details, like what nutrients the black smokers are providing to boost phytoplankton growth and how feasible it would be to replicate the mix.
Nitrogen is not the limiting nutrient in LNLC waters. Phytoplankton is a catch bin category that includes all sorts of photosynthetic organisms including cyanobacteria (also known as blue-green algae) which fix nitrogen. The phytoplankton in the open ocean already can fix nitrogen and carbon from the air. Their growth is not limited by availability of nitrogen. It's iron and phosphorous that are typically limiting.
Anyone who lives on a lake knows that fertilizer runoff leads to (blue-green) algae blooms because the fertilizer provides phosphorous, which is the limiting nutrient in this case.
We already know from iron fertilization experiments that adding iron to LC waters will produce growth. That is basically what you are proposing here.
It's true that iron is limiting on diazotrophs, because nitrogenase needs quite a lot of iron. But what limits the broader phytoplankton community — is fixed nitrogen.
Haven't heard about that guy, was a fun read. But the role of Iron is as old as the iron age. The effect of iron is nothing but spectacular, even in shallow waters. Anywhere rich in iron will be rich in Mussels that is a staple food in the Atlantic.
Part of the problem is that Sperm Whale is a Keystone species that sleep in the surface as a direct danger to ships. And otherwise dive deep, eat squid and shit in surface, unable to at extreme depth.
No matter what you do, you will not be able to counter negative impacts on predatory fishing outside Chile on squid and other deep sea food sources.
But probably a topic that needs to be looked into. In Norway there is interest in an estimated 50 million metric tons of Salmon shits as bio active marine nitrogen source with possible value.
Can't help with another tidbit, it's difficult to work out exactly how much each whale contribute as a carbon dump. Down to being metric tons of carbon that go to the seabed and provide carbon to that ecosystem or just sink into oxygen poor sea floor.
But somewhat confident it's absolutely necessary starting point. Nobody is going to be brave enough without being firmly rooted and anchored in Keystone species. As industrial and pure chemical measures have higher risks due promotering invasive species that absolutely will not have a Keystone effect.
While true, abd some may think differently about Moby Dick. But a narrative that sounds be easy to sell, is that we need more Sperm Whales, others may also have Keystone roles. Alas, it's important work, diving down to the Atlantic ridge abd taking massive whale shits in the surface. It may not be wrong to support it and make sure the ecosystem survive with the Keystone species.
Great article, thanks so much! I’d heard some of the discussion of HNLC iron distribution before but this is very hopeful news. Thanks for laying this out so clearly.
The key thing you are trying to achieve is fixing carbon. That is net conversion a kg of atmospheric carbon into two kg (dry wt) of biomass, which sinks to the bottom.
The four biggest components of biomass are C, H, O and N. Water provides the H and O, and CO2 provides the carbon. For cyanobacteria, atmospheric nitrogen provides the N. For other phytoplankton, nitrate that leaks out of the cyanobacterial provides the N.
But biomass also contains other components, P, S, Mg, Fe, Co, and a bunch of other minerals, which they need to get in their diet, just as we do. Phytoplanton contains a lot of diatoms, so silica is also a nutrient (but this may simply be because hydrovents contain a lot of silica, so you get a lot of diatoms). We are talking a natural process--we aren't in a bioreactor, where we have better control over things--so things are going to be complicated.
SO for every ton of carbon you sequester you will need to provide some of these other nutrients, Phosphorous likely, and certainly iron. Perhaps others. You can figure you will need about 1 kg of phosphorous for every 50-100 kg of carbon you sequester. There's plenty of sulfur in seawater so that's not problem.
Thank you for this post. Fascinating and new to me, although I've been paying some attention to carbon removal technology since I wrote an article (and then a short book) about direct air capture of CO2 for FORTUNE magazine in 2011. I'm sure you know that there was a startup company called Planktos that intended to make a business out of ocean iron fertilization at about that time. I hope that in a future post you will write about (1) the costs of this technology and (2) the business model, if any, for bringing it to scale and (3) the politics. Surely there will be opposition from environmentalists but by now I hope that the more mainstream green groups recognize the need for CDR.
I've written about cost —at a high level of abstraction— here: https://www.onepercentbrighter.com/p/the-two-freebies-driving-phytoplankton
But of course it's impossible to know how much this is really going to cost until you go and do it. Cost discovery is the far end of a process of learning-by-doing and economies of scale.
For now all we can really say is that the *materials* to do this cost almost nothing (pennies per ton of CO2 in an iron-only scenario, less than $5 per ton in an iron+phosphates scenario). But of course the materials aren't really the point, it's the deployment and the monitoring, reporting and verification that cost money. How much? Your guess is as good as mine.
The business model and the politics are deep waters, too. I spend all my time thinking about this stuff. More to come for sure.
I believe there are desert areas below sea level. I remember reading about such a place in Mexico. I was thinking you could pump in ocean water to create a large salt water lake. You could experiment with these proposals there. If it worked the lake could absorb a lot of co2 without affecting the ocean ecosystem.
Yes!! The biggest one is in Egypt — a dried up former sea known as the Qattara Depression. I talked to some guys working on this. They want to dig a ditch from the Mediterranean to bring water over, with a big hydro-electric dam in the middle. It's pretty cool. An added plus is that the evaporation from the project should increase rainfall just east of it, across the Sinai and into Arabia, which are all places that could use more rain.
https://news.mongabay.com/2025/12/can-we-create-new-inland-seas-to-lower-sea-level-rise-interview-with-researcher-amir-aghakouchak/
There are sites in Australia that are even larger, where this could also be tried. It's very cool stuff.
(Haven't heard of the one in Mexico though...)
There was an example in the interior of Australia. Many decades ago some entrepreneurs started a project to pipe sea water to a below sea level area of desert in an effort to build an inland sea and even engineer more rainfall on the continent. The project was halted as it caused salt increases in groundwater that ruined grazing land and because the corrosive effect of salt and its depositions made maintaining the canals too expensive.
Is the only proposed human intervention adding iron to LNLC regions? Or are other steps necessary, like modifying trichodesmium cultivars for survival in LNLC habitats?
Edit: upon further reading, the implication seems to be that the only thing the hydrothermal vents added the example was iron. I think it could be said clearer though that there are LNLC areas, that shallow hydrothermal vents add just iron, leaving areas high in iron but low in nitrates and phosphates, and that results in trichodesmium blooms, and that this might extend to LNLC iron fertilization in general. It would be useful to have a clear takeaway message of “iron fertilization in HNLC areas may have problems, but these are probably solved by just fertilizing LNLC areas instead”.
I mean, it's such early days. The researchers I talk to tend to think trichodesmium are hardy old buggers and don't need any genetic messing-with to thrive, just nutrients. But who knows where that debate will be 10-20 years from now.
The research on those shallow vents seems to find that iron is the main thing making a difference, but again this needs farther study. Of course a natural process like a vent isn't going to be releasing a controlled flow of pure minerals, and there's certainly other stuff mixed in with the iron, and probably some phosphates too. I know it feels like a cop out when scientists say "we need another study" but in this case...man, we really do need more study.
Ok, yes, I didn't know about this version of carbon capture. In your effort to tell a good story though you left out some important details, like what nutrients the black smokers are providing to boost phytoplankton growth and how feasible it would be to replicate the mix.
Nitrogen is not the limiting nutrient in LNLC waters. Phytoplankton is a catch bin category that includes all sorts of photosynthetic organisms including cyanobacteria (also known as blue-green algae) which fix nitrogen. The phytoplankton in the open ocean already can fix nitrogen and carbon from the air. Their growth is not limited by availability of nitrogen. It's iron and phosphorous that are typically limiting.
Anyone who lives on a lake knows that fertilizer runoff leads to (blue-green) algae blooms because the fertilizer provides phosphorous, which is the limiting nutrient in this case.
We already know from iron fertilization experiments that adding iron to LC waters will produce growth. That is basically what you are proposing here.
It's true that iron is limiting on diazotrophs, because nitrogenase needs quite a lot of iron. But what limits the broader phytoplankton community — is fixed nitrogen.
On this point, Bonnet et al. 2023's paper is...well, nothing in science is ever conclusive, but this was pretty close to conclusive -> https://www.science.org/doi/10.1126/science.abq4654
For sure, you do end up needing to add iron anyway, but as an intermediary step to get Nitrogen fixation going.
@Quico Toro, I call you Ishmael, and the best if luck with important work. And hope this hook abd angle will help.
Haven't heard about that guy, was a fun read. But the role of Iron is as old as the iron age. The effect of iron is nothing but spectacular, even in shallow waters. Anywhere rich in iron will be rich in Mussels that is a staple food in the Atlantic.
Part of the problem is that Sperm Whale is a Keystone species that sleep in the surface as a direct danger to ships. And otherwise dive deep, eat squid and shit in surface, unable to at extreme depth.
No matter what you do, you will not be able to counter negative impacts on predatory fishing outside Chile on squid and other deep sea food sources.
But probably a topic that needs to be looked into. In Norway there is interest in an estimated 50 million metric tons of Salmon shits as bio active marine nitrogen source with possible value.
Can't help with another tidbit, it's difficult to work out exactly how much each whale contribute as a carbon dump. Down to being metric tons of carbon that go to the seabed and provide carbon to that ecosystem or just sink into oxygen poor sea floor.
But somewhat confident it's absolutely necessary starting point. Nobody is going to be brave enough without being firmly rooted and anchored in Keystone species. As industrial and pure chemical measures have higher risks due promotering invasive species that absolutely will not have a Keystone effect.
While true, abd some may think differently about Moby Dick. But a narrative that sounds be easy to sell, is that we need more Sperm Whales, others may also have Keystone roles. Alas, it's important work, diving down to the Atlantic ridge abd taking massive whale shits in the surface. It may not be wrong to support it and make sure the ecosystem survive with the Keystone species.
Great article, thanks so much! I’d heard some of the discussion of HNLC iron distribution before but this is very hopeful news. Thanks for laying this out so clearly.
Is anyone working on this? Academia, nonprofits, etc?
Yes we are! (Details on this in posts to come...)
Great. However not convinced about runaway climate change.