Oceans as climate change allies

If you had asked him a decade ago, marine biogeochemist Kai Schulz of Southern Cross University would have distanced himself from work probing how the oceans could be engineered to absorb more carbon dioxide. “I thought it would be kind of ridiculous to have a billion-dollar industry that is emitting CO₂ and then create another billion-dollar industry that takes the CO₂ out of the atmosphere,” he says.

But as greenhouse gas emissions continued to increase and global temperatures continued to climb, his opinion began to change. Like many ocean researchers, Schulz began to wonder if the ocean, already a crucial ally in humanity’s fight against climate change, could be coaxed to do more.

A recent Intergovernmental Panel on Climate Change (IPCC) report indicates that significant emission cuts alone will not prevent average global temperatures from shooting past 1.5 °C above preindustrial averages. Some portion of carbon dioxide must be removed from the atmosphere to offset industries that are difficult to decarbonize and maintain a livable climate.

Boosting the ocean’s innate ability to soak up and store carbon dioxide is one of many carbon dioxide removal (CDR) approaches that scientists and policymakers are investigating. Research teams from around the world are working to establish methods of monitoring, reporting, and verifying the efficacy of adding alkalinity to seawater for CDR (State Planet 2023, DOI: 10.5194/sp-2-oae2023-12-2023).

Ocean carbonate chemistry

The ocean is one of the largest net sinks of carbon on the planet, soaking up more than a quarter of carbon dioxide emitted by humans annually (Earth Syst. Sci. Data 2022, DOI: 10.5194/essd-14-4811-2022). This impressive ability is due largely to the carbonate chemistry occurring under the surface. As carbon dioxide is exchanged between air and sea, some of the dissolved gas reacts with water and forms carbonic acid. The weak acid dissociates into a buffer system of bicarbonate (HCO₃^–) and carbonate (CO₃^2–) that maintains the ocean’s natural pH just above 8. After carbon is trapped in these ions, it stays there for tens of millennia before it’s released as carbon dioxide.

The dissolution of carbonic acid also releases protons, making the water more acidic. But as naturally occurring alkaline minerals dissolve and release negative ions into the water, some acidity is neutralized. This shifts the carbonate system toward bicarbonate, and the nudge makes space for more atmospheric carbon dioxide to be absorbed into the water.

This natural process of increasing alkalinity occurs over hundreds or thousands of years, according to a report from the National Academies of Sciences, Engineering, and Medicine (2022, DOI: 10.17226/26278). Scientists think they could speed up the process by adding alkaline substances directly to seawater in a technique termed ocean alkalinity enhancement (OAE).

Measuring success

Monitoring how much carbon dioxide is removed from the atmosphere after an OAE deployment will be a challenge. “You have to wait months for the water to potentially equilibrate with the atmosphere,” says David Ho, professor of oceanography at the University of Hawaii at Manoa and cofounder of the nonprofit [C]Worthy. By the time the alkalinity-enhanced water body has absorbed the anticipated extra amount of carbon dioxide, it will have flowed far from where the treatment occurred. A direct measurement of carbon absorbed will be impossible in practice.

Modeling can fill in the blank, Ho says. Researchers can measure the chemical perturbations in water caused by the initial addition of alkalinity. Then they can use models to predict how these small-scale changes will affect the larger area as the water moves, he explains. Models can also provide insight into what would have happened if researchers had not treated the water, giving scientists something to compare to. Essentially, modeling will enable researchers to tell whether OAE works in the real world, Ho says.

Unfortunately, because global carbon dioxide emissions continue to climb, full-scale deployment of OAE or other carbon removal technologies is “like setting money on fire,” Ho says. He imagines CDR as a time machine. “We keep emitting CO₂ at more than 40 billion tons every year,” he says. “If you remove 1 million tons in a year, that time machine takes you back about 13 min.” And current carbon removal technologies, including OAE, aren’t nearly that effective yet.

This has not deterred investment in the private carbon removal market. Investment is vital both to decarbonize and find effective CDR strategies. The two go hand in hand: the more emissions are cut, the more humanity gains from carbon removal, Ho says.

Mesocosm and microcosm laboratories

The ocean is more than just a salty buffer solution. In many places, it’s teeming with life. Researchers need evidence that ocean-dwelling communities can weather alkalinity changes before anyone attempts large-scale OAE deployment.

Schulz is working with researchers at the German Geomar Helmholtz Center for Ocean Research Kiel to collect such evidence. The scientists use containers of seawater full of natural plankton communities for their OAE tests. The tiny species make up the bottom of the food web. If they can’t survive OAE treatment, animals higher on the food web will lose their daily meals.

The vats Geomar researchers use are known as mesocosms or microcosms, depending on size. Mesocosm containers hold thousands of liters of water isolated from the surrounding sea. The larger container studies are designed to mimic field trials but in a more controlled environment than the open ocean. The containers float near shore and experience the same weather conditions as the surrounding water.

Microcosms, in contrast, usually contain less than 100 L of water. The bottles can be kept indoors, where researchers carefully control conditions like light and temperature. Such control enables standardization. In fact, 19 research groups worldwide—including Geomar scientists—are participating in the first globally coordinated OAE study using microcosms. The standardized study, Ocean Alkalinity Enhancement Pelagic Impact Intercomparison Project (OAEPIIP), aims to provide insight into the effects of OAE on plankton (Biogeosciences 2024, DOI: 10.5194/bg-21-3665-2024).

These experiments can answer many questions about OAE and are a vital step before moving to real field trials, Schulz says. “Ideally, you try it on a small-scale bottle or mesocosm to make sure that everything doesn’t die,” he adds.

Some of Schulz’s experiments have revealed that increasing the alkalinity of seawater appears to change how plankton grow in the spring (EGUsphere 2025, DOI: 10.5194/egusphere-2025-524). “Timing of the blooming was delayed towards high alkalinities,” he explains. It’s not clear if this delay will affect animals higher on the food web, a question Schulz hopes to answer in future studies that will add fish larvae to the system.

With closed-system experiments, researchers can also identify potentially undesirable geochemical effects of increasing seawater’s alkalinity, such as calcium carbonate precipitation. Runaway solid precipitation can remove negative ions from the water, thus limiting the efficacy of the OAE treatment (Biogeosciences 2022, DOI: 10.5194/bg-19-3537-2022). Such experiments have already yielded important insights.

According to Schulz, precipitation occurs at a lower threshold when scientists use particle-based alkalinity enhancers as opposed to alkaline solutions. This is because particles, such as crushed alkaline minerals, serve as a nucleation surface.

Thus far, the findings suggest that harmful impacts of OAE treatment will be localized. Schulz likens it to freshwater outflows into the ocean: ocean creatures cannot thrive in the area directly around the outflow, but communities farther away are fine.

Overall, Schulz says more testing, in closed systems and small field trials, is necessary to have a scientifically based discussion concerning OAE deployment. The way Germany has decided to comply with the London Convention—international governance aiming to prevent marine pollution—prevents Geomar scientists from releasing alkaline substances into open water, Schulz says. But elsewhere, others have moved OAE experiments into the field.

Alkaline minerals down under

Marianne Pelletier has spent many hours breathing underwater in the name of science. But her most recent dive off the coast of Tasmania stands out. “I felt more like I was doing something to really progress a field, rather than just counting some fish on the reef,” she says. Her goal: measure the impacts of particle-based OAE on the local ecosystem.

In the water, Pelletier floated about 4 m beneath the surface, filming her research partner, Damon Britton, as he carefully cracked open a vial containing a slurry of crushed limestone. The smallest grains floated away as he tried to spread the alkaline mineral evenly on approximately 1.5 × 1.5 m plots, but the larger, micrometer-sized bits made it to the sediment. Britton carefully raked them in to help prevent the pieces from immediately washing away. The divers would follow a similar procedure with crushed olivine, a silicate mineral, in another, nearby plot.

The team returned to the dive site five times to collect samples of sediment and pore water—the water between the sand grains. As the deposited minerals began to dissolve, the team expected to see changes in the pH and alkalinity of the pore water.

This experiment is far smaller than what deployment might look like in the future, Britton says. That would likely involve ships releasing thousands of metric tons of ground minerals into the water. Some companies are moving ahead with much larger field trials.

Small-scale field studies are a vital step in OAE research, says Lennart Bach, leader of the University of Tasmania team. Self-described as “just the boat driver” on this particular field project—he also took pH measurements and helped make decisions but says Britton led the research effort—Bach started his career investigating the effect of ocean acidification on plankton. After discovering how many climate scenarios required CDR in addition to drastic cuts in carbon dioxide emissions, Bach started looking into OAE. In addition to his work in Tasmania, he leads the international OAEPIIP project.

Not only can field studies give insight into ecosystem effects, but they may also help researchers understand how added alkalinity affects the ocean’s natural carbonate cycle (Biogeosciences 2024, DOI: 10.5194/bg-21-261-2024). “You never can reproduce the complexity of the real world in a lab,” Bach says. Small trials allow researchers to answer fundamental questions about the real-world safety and efficacy of OAE without putting large swaths of watery habitat at risk. “Furthermore, if OAE remains in the lab, it will be regarded as science fiction forever,” he adds.

The researchers brought the samples from the field to the lab where they combed through the sediment looking for worms and other benthic animals. They also measured the pH, alkalinity, and salinity of the pore water. The group is still analyzing the data, but so far, it seems that sediment dwelling species aren’t particularly bothered by the mineral addition.

This won’t be the last OAE field trial Pelletier and Britton perform. Next summer, “we’ll do something probably a bit different; maybe use a different mineral, maybe on a different habitat,” Pelletier says.

Liquid alkalinity in the field

In the summer of 2023, a world away from Tasmania, Adam Subhas watched from the back of a research vessel as a plume of brilliant magenta water flowed in the sea south of Martha’s Vineyard, Massachusetts. “It was a pretty big moment,” he recalls. The rhodamine-dyed water would ultimately help Subhas monitor the effects of using liquid alkalinity for OAE.

Before performing experiments with alkalinity, the Woods Hole Oceanographic Institution (WHOI) scientist and his colleagues needed find out whether they could track and measure the chemistry of the colored water body. The experiment was the first of three field trials that Subhas initially proposed in a project called Locking Ocean Carbon in the Northeast Shelf and Slope, or LOC-NESS.

“We had initially planned to conduct an experiment south of Martha’s Vineyard last summer,” Subhas says. But unexpected scheduling issues within the fleet of research boats kept the experiment docked. With the extra time, “we were able to take another look at our project scope and plans,” Subhas says.

The delay gave the researchers time to directly engage with local community members—including fishers, members of local Indigenous nations, and other residents—and incorporate their feedback into the updated permit application. “The fishermen really did highlight that they were interested in seeing the effects of elevated alkalinity on fish larvae,” Subhas says.

The team also had time to run experiments in a 10 million L open-air facility in New Jersey. “That was not part of the original plan,” Subhas says. The experiments gave the researchers the opportunity to further validate their engineering design ahead of the next planned field trial. Those data, combined with the results from the first, dye-only field test, give Subhas that the confidence that the team will be able to quantify the amount of carbon dioxide removed from the air by the added alkalinity (EGUsphere 2025, DOI: 10.5194/egusphere-2025-1348).

This hypothesis will be put to the test this summer in Wilkinson Basin, off the coast of Cape Cod, where Subhas plans to mix about 62,500 L of sodium hydroxide solution—their alkalinity of choice—into the water over the course of about 4 h. The researchers chose the area to minimize the impact to fishing and the marine environment, and to satisfy the physical and chemical criteria of the project.

As a strong base, sodium hydroxide completely dissociates in water to form sodium cations and hydroxide anions—unadulterated alkalinity. “We can get that alkalinity into seawater and make a patch of water that we can follow with a ship relatively easily,” Subhas says. Solid sources of alkalinity such as minerals, on the other hand, could settle out of the water column before they dissolve into alkaline ions, and they could also add undesirable trace elements to the water.

After the alkaline solution is released, the measurements will begin. The boat will tow a winged underwater vehicle decked out with sensors to monitor pH, fluorescence, oxygen concentration, temperature, and salinity. The team will deploy GPS buoys that rise with the tides and drift with the currents to monitor how the water moves. A lab within the ship will enable the researchers to measure the partial pressure of carbon dioxide in water samples and compare it with that of the atmosphere. And the team will monitor plankton, fish and lobster larvae, and other tiny drifting species.

“We’re going to be doing this 24 h a day for literally 7 days. We have two teams of researchers that do 12 h shifts, and we just go back and forth,” Subhas says.

With a grant from the US National Oceanic and Atmospheric Administration (NOAA), the LOC-NESS team is also deploying autonomous vehicles to monitor the water in the weeks before, during, and after the time his team is on the boat. “Even though we’re off the ship and back on land, these gliders are going to stay out, continually monitoring the area,” he says.

Environmental advocacy groups, however, are skeptical of the operation. In June 2024, Friends of the Earth published a news release in strong opposition to the original LOC-NESS proposal. The document questions the safety of adding sodium hydroxide to waters where endangered animals, such as right whales and leatherback turtles, swim and live.

“Pure sodium hydroxide, that’s very bad for you. You don’t want to be anywhere near that,” Ho of [C]Worthy says. But the sodium hydroxide solution the LOC-NESS team will use is already diluted and will quickly dilute further, he says. And the volume of sodium hydroxide that will be used in the field trial is far less than is used in the US to control the pH of drinking water. Ho is not directly involved in Subhas’s study, but the OAE research community is relatively small, and Ho knows of the work.

James Kerry, a senior marine and climate scientist at the nonprofit OceanCare and senior research fellow at James Cook University, is not convinced that the LOC-NESS team will be able to answer key questions about the efficacy and safety of large-scale OAE deployments. “I know the WHOI researchers are deploying lots of different techniques to try and monitor their impact,” he says, but this experiment is relatively small, and the real-world marine environment is complex. Teasing out cause-and-effect in the data will be incredibly challenging.

Confidence in the efficacy of OAE will ultimately come down to how much one can trust the models field data are plugged into, Kerry says. And considering the scale of climate-relevant deployment—which will require new international governance and vast amounts of alkalinity sources in the form of mined minerals or manufactured chemical bases—he does not believe OAE is a genuine climate solution.

Subhas is still waiting to receive the final permit from the US Environmental Protection Agency for the LOC-NESS trial planned for late this summer. The team repeated the entire permitting process after having canceled their planned trial last summer, and the most recent public comment period closed in February. Now, permitting is “on the EPA’s timeline,” Subhas says.

Building an international coalition of scientists

For most of his career advising foundations on marine conservation, Antonius Gagern, like Schulz, thought marine CDR was a bad idea. “Why would you want to increase the amount of CO₂ that is going into the ocean, knowing that acidification is a problem?” he asks.

But when Gagern dove into the science in 2018 and learned more about the chemistry of marine CDR, his opinion changed. Now he’s the executive director of the nonprofit Carbon to Sea Initiative, one of the largest private funders in the space. “My entire focus for the last 6 years or so has been building the philanthropic response for marine CDR,” he says.

“We have made approximately $30 million in grants to universities, research institutes, and start-ups around the world,” Gagern says. To this end, they’ve provided funds to the LOC-NESS project, the OAEPIIP project, and [C]Worthy, among others.

Not only does the Carbon to Sea Initiative fund research, but the nonprofit also brings the research community together by hosting annual science meetings. “The future for us is going to be really focused on continuing building consensus on viability and desirability of OAE,” Gagern says.

If you had asked him a decade ago, marine biogeochemist Kai Schulz of Southern Cross University would have distanced himself from work probing how the oceans could be engineered to absorb more carbon dioxide. “I thought it would be kind of ridiculous to have a billion-dollar industry that is emitting CO₂ and then create another billion-dollar industry that takes the CO₂ out of the atmosphere,” he says.

But as greenhouse gas emissions continued to increase and global temperatures continued to climb, his opinion began to change. Like many ocean researchers, Schulz began to wonder if the ocean, already a crucial ally in humanity’s fight against climate change, could be coaxed to do more.

A recent Intergovernmental Panel on Climate Change (IPCC) report indicates that significant emission cuts alone will not prevent average global temperatures from shooting past 1.5 °C above preindustrial averages. Some portion of carbon dioxide must be removed from the atmosphere to offset industries that are difficult to decarbonize and maintain a livable climate.

Boosting the ocean’s innate ability to soak up and store carbon dioxide is one of many carbon dioxide removal (CDR) approaches that scientists and policymakers are investigating. Research teams from around the world are working to establish methods of monitoring, reporting, and verifying the efficacy of adding alkalinity to seawater for CDR (State Planet 2023, DOI: 10.5194/sp-2-oae2023-12-2023).

Ocean carbonate chemistry

The ocean is one of the largest net sinks of carbon on the planet, soaking up more than a quarter of carbon dioxide emitted by humans annually (Earth Syst. Sci. Data 2022, DOI: 10.5194/essd-14-4811-2022). This impressive ability is due largely to the carbonate chemistry occurring under the surface. As carbon dioxide is exchanged between air and sea, some of the dissolved gas reacts with water and forms carbonic acid. The weak acid dissociates into a buffer system of bicarbonate (HCO₃^–) and carbonate (CO₃^2–) that maintains the ocean’s natural pH just above 8. After carbon is trapped in these ions, it stays there for tens of millennia before it’s released as carbon dioxide.

The dissolution of carbonic acid also releases protons, making the water more acidic. But as naturally occurring alkaline minerals dissolve and release negative ions into the water, some acidity is neutralized. This shifts the carbonate system toward bicarbonate, and the nudge makes space for more atmospheric carbon dioxide to be absorbed into the water.

This natural process of increasing alkalinity occurs over hundreds or thousands of years, according to a report from the National Academies of Sciences, Engineering, and Medicine (2022, DOI: 10.17226/26278). Scientists think they could speed up the process by adding alkaline substances directly to seawater in a technique termed ocean alkalinity enhancement (OAE).

Measuring success

Monitoring how much carbon dioxide is removed from the atmosphere after an OAE deployment will be a challenge. “You have to wait months for the water to potentially equilibrate with the atmosphere,” says David Ho, professor of oceanography at the University of Hawaii at Manoa and cofounder of the nonprofit [C]Worthy. By the time the alkalinity-enhanced water body has absorbed the anticipated extra amount of carbon dioxide, it will have flowed far from where the treatment occurred. A direct measurement of carbon absorbed will be impossible in practice.

Modeling can fill in the blank, Ho says. Researchers can measure the chemical perturbations in water caused by the initial addition of alkalinity. Then they can use models to predict how these small-scale changes will affect the larger area as the water moves, he explains. Models can also provide insight into what would have happened if researchers had not treated the water, giving scientists something to compare to. Essentially, modeling will enable researchers to tell whether OAE works in the real world, Ho says.

Unfortunately, because global carbon dioxide emissions continue to climb, full-scale deployment of OAE or other carbon removal technologies is “like setting money on fire,” Ho says. He imagines CDR as a time machine. “We keep emitting CO₂ at more than 40 billion tons every year,” he says. “If you remove 1 million tons in a year, that time machine takes you back about 13 min.” And current carbon removal technologies, including OAE, aren’t nearly that effective yet.

This has not deterred investment in the private carbon removal market. Investment is vital both to decarbonize and find effective CDR strategies. The two go hand in hand: the more emissions are cut, the more humanity gains from carbon removal, Ho says.

Mesocosm and microcosm laboratories

The ocean is more than just a salty buffer solution. In many places, it’s teeming with life. Researchers need evidence that ocean-dwelling communities can weather alkalinity changes before anyone attempts large-scale OAE deployment.

Schulz is working with researchers at the German Geomar Helmholtz Center for Ocean Research Kiel to collect such evidence. The scientists use containers of seawater full of natural plankton communities for their OAE tests. The tiny species make up the bottom of the food web. If they can’t survive OAE treatment, animals higher on the food web will lose their daily meals.

The vats Geomar researchers use are known as mesocosms or microcosms, depending on size. Mesocosm containers hold thousands of liters of water isolated from the surrounding sea. The larger container studies are designed to mimic field trials but in a more controlled environment than the open ocean. The containers float near shore and experience the same weather conditions as the surrounding water.

Microcosms, in contrast, usually contain less than 100 L of water. The bottles can be kept indoors, where researchers carefully control conditions like light and temperature. Such control enables standardization. In fact, 19 research groups worldwide—including Geomar scientists—are participating in the first globally coordinated OAE study using microcosms. The standardized study, Ocean Alkalinity Enhancement Pelagic Impact Intercomparison Project (OAEPIIP), aims to provide insight into the effects of OAE on plankton (Biogeosciences 2024, DOI: 10.5194/bg-21-3665-2024).

These experiments can answer many questions about OAE and are a vital step before moving to real field trials, Schulz says. “Ideally, you try it on a small-scale bottle or mesocosm to make sure that everything doesn’t die,” he adds.

Some of Schulz’s experiments have revealed that increasing the alkalinity of seawater appears to change how plankton grow in the spring (EGUsphere 2025, DOI: 10.5194/egusphere-2025-524). “Timing of the blooming was delayed towards high alkalinities,” he explains. It’s not clear if this delay will affect animals higher on the food web, a question Schulz hopes to answer in future studies that will add fish larvae to the system.

With closed-system experiments, researchers can also identify potentially undesirable geochemical effects of increasing seawater’s alkalinity, such as calcium carbonate precipitation. Runaway solid precipitation can remove negative ions from the water, thus limiting the efficacy of the OAE treatment (Biogeosciences 2022, DOI: 10.5194/bg-19-3537-2022). Such experiments have already yielded important insights.

According to Schulz, precipitation occurs at a lower threshold when scientists use particle-based alkalinity enhancers as opposed to alkaline solutions. This is because particles, such as crushed alkaline minerals, serve as a nucleation surface.

Thus far, the findings suggest that harmful impacts of OAE treatment will be localized. Schulz likens it to freshwater outflows into the ocean: ocean creatures cannot thrive in the area directly around the outflow, but communities farther away are fine.

Overall, Schulz says more testing, in closed systems and small field trials, is necessary to have a scientifically based discussion concerning OAE deployment. The way Germany has decided to comply with the London Convention—international governance aiming to prevent marine pollution—prevents Geomar scientists from releasing alkaline substances into open water, Schulz says. But elsewhere, others have moved OAE experiments into the field.

Alkaline minerals down under

Marianne Pelletier has spent many hours breathing underwater in the name of science. But her most recent dive off the coast of Tasmania stands out. “I felt more like I was doing something to really progress a field, rather than just counting some fish on the reef,” she says. Her goal: measure the impacts of particle-based OAE on the local ecosystem.

In the water, Pelletier floated about 4 m beneath the surface, filming her research partner, Damon Britton, as he carefully cracked open a vial containing a slurry of crushed limestone. The smallest grains floated away as he tried to spread the alkaline mineral evenly on approximately 1.5 × 1.5 m plots, but the larger, micrometer-sized bits made it to the sediment. Britton carefully raked them in to help prevent the pieces from immediately washing away. The divers would follow a similar procedure with crushed olivine, a silicate mineral, in another, nearby plot.

The team returned to the dive site five times to collect samples of sediment and pore water—the water between the sand grains. As the deposited minerals began to dissolve, the team expected to see changes in the pH and alkalinity of the pore water.

This experiment is far smaller than what deployment might look like in the future, Britton says. That would likely involve ships releasing thousands of metric tons of ground minerals into the water. Some companies are moving ahead with much larger field trials.

Small-scale field studies are a vital step in OAE research, says Lennart Bach, leader of the University of Tasmania team. Self-described as “just the boat driver” on this particular field project—he also took pH measurements and helped make decisions but says Britton led the research effort—Bach started his career investigating the effect of ocean acidification on plankton. After discovering how many climate scenarios required CDR in addition to drastic cuts in carbon dioxide emissions, Bach started looking into OAE. In addition to his work in Tasmania, he leads the international OAEPIIP project.

Not only can field studies give insight into ecosystem effects, but they may also help researchers understand how added alkalinity affects the ocean’s natural carbonate cycle (Biogeosciences 2024, DOI: 10.5194/bg-21-261-2024). “You never can reproduce the complexity of the real world in a lab,” Bach says. Small trials allow researchers to answer fundamental questions about the real-world safety and efficacy of OAE without putting large swaths of watery habitat at risk. “Furthermore, if OAE remains in the lab, it will be regarded as science fiction forever,” he adds.

The researchers brought the samples from the field to the lab where they combed through the sediment looking for worms and other benthic animals. They also measured the pH, alkalinity, and salinity of the pore water. The group is still analyzing the data, but so far, it seems that sediment dwelling species aren’t particularly bothered by the mineral addition.

This won’t be the last OAE field trial Pelletier and Britton perform. Next summer, “we’ll do something probably a bit different; maybe use a different mineral, maybe on a different habitat,” Pelletier says.

Liquid alkalinity in the field

In the summer of 2023, a world away from Tasmania, Adam Subhas watched from the back of a research vessel as a plume of brilliant magenta water flowed in the sea south of Martha’s Vineyard, Massachusetts. “It was a pretty big moment,” he recalls. The rhodamine-dyed water would ultimately help Subhas monitor the effects of using liquid alkalinity for OAE.

Before performing experiments with alkalinity, the Woods Hole Oceanographic Institution (WHOI) scientist and his colleagues needed find out whether they could track and measure the chemistry of the colored water body. The experiment was the first of three field trials that Subhas initially proposed in a project called Locking Ocean Carbon in the Northeast Shelf and Slope, or LOC-NESS.

“We had initially planned to conduct an experiment south of Martha’s Vineyard last summer,” Subhas says. But unexpected scheduling issues within the fleet of research boats kept the experiment docked. With the extra time, “we were able to take another look at our project scope and plans,” Subhas says.

The delay gave the researchers time to directly engage with local community members—including fishers, members of local Indigenous nations, and other residents—and incorporate their feedback into the updated permit application. “The fishermen really did highlight that they were interested in seeing the effects of elevated alkalinity on fish larvae,” Subhas says.

The team also had time to run experiments in a 10 million L open-air facility in New Jersey. “That was not part of the original plan,” Subhas says. The experiments gave the researchers the opportunity to further validate their engineering design ahead of the next planned field trial. Those data, combined with the results from the first, dye-only field test, give Subhas that the confidence that the team will be able to quantify the amount of carbon dioxide removed from the air by the added alkalinity (EGUsphere 2025, DOI: 10.5194/egusphere-2025-1348).

This hypothesis will be put to the test this summer in Wilkinson Basin, off the coast of Cape Cod, where Subhas plans to mix about 62,500 L of sodium hydroxide solution—their alkalinity of choice—into the water over the course of about 4 h. The researchers chose the area to minimize the impact to fishing and the marine environment, and to satisfy the physical and chemical criteria of the project.

As a strong base, sodium hydroxide completely dissociates in water to form sodium cations and hydroxide anions—unadulterated alkalinity. “We can get that alkalinity into seawater and make a patch of water that we can follow with a ship relatively easily,” Subhas says. Solid sources of alkalinity such as minerals, on the other hand, could settle out of the water column before they dissolve into alkaline ions, and they could also add undesirable trace elements to the water.

After the alkaline solution is released, the measurements will begin. The boat will tow a winged underwater vehicle decked out with sensors to monitor pH, fluorescence, oxygen concentration, temperature, and salinity. The team will deploy GPS buoys that rise with the tides and drift with the currents to monitor how the water moves. A lab within the ship will enable the researchers to measure the partial pressure of carbon dioxide in water samples and compare it with that of the atmosphere. And the team will monitor plankton, fish and lobster larvae, and other tiny drifting species.

“We’re going to be doing this 24 h a day for literally 7 days. We have two teams of researchers that do 12 h shifts, and we just go back and forth,” Subhas says.

With a grant from the US National Oceanic and Atmospheric Administration (NOAA), the LOC-NESS team is also deploying autonomous vehicles to monitor the water in the weeks before, during, and after the time his team is on the boat. “Even though we’re off the ship and back on land, these gliders are going to stay out, continually monitoring the area,” he says.

Environmental advocacy groups, however, are skeptical of the operation. In June 2024, Friends of the Earth published a news release in strong opposition to the original LOC-NESS proposal. The document questions the safety of adding sodium hydroxide to waters where endangered animals, such as right whales and leatherback turtles, swim and live.

“Pure sodium hydroxide, that’s very bad for you. You don’t want to be anywhere near that,” Ho of [C]Worthy says. But the sodium hydroxide solution the LOC-NESS team will use is already diluted and will quickly dilute further, he says. And the volume of sodium hydroxide that will be used in the field trial is far less than is used in the US to control the pH of drinking water. Ho is not directly involved in Subhas’s study, but the OAE research community is relatively small, and Ho knows of the work.

James Kerry, a senior marine and climate scientist at the nonprofit OceanCare and senior research fellow at James Cook University, is not convinced that the LOC-NESS team will be able to answer key questions about the efficacy and safety of large-scale OAE deployments. “I know the WHOI researchers are deploying lots of different techniques to try and monitor their impact,” he says, but this experiment is relatively small, and the real-world marine environment is complex. Teasing out cause-and-effect in the data will be incredibly challenging.

Confidence in the efficacy of OAE will ultimately come down to how much one can trust the models field data are plugged into, Kerry says. And considering the scale of climate-relevant deployment—which will require new international governance and vast amounts of alkalinity sources in the form of mined minerals or manufactured chemical bases—he does not believe OAE is a genuine climate solution.

Subhas is still waiting to receive the final permit from the US Environmental Protection Agency for the LOC-NESS trial planned for late this summer. The team repeated the entire permitting process after having canceled their planned trial last summer, and the most recent public comment period closed in February. Now, permitting is “on the EPA’s timeline,” Subhas says.

Building an international coalition of scientists

For most of his career advising foundations on marine conservation, Antonius Gagern, like Schulz, thought marine CDR was a bad idea. “Why would you want to increase the amount of CO₂ that is going into the ocean, knowing that acidification is a problem?” he asks.

But when Gagern dove into the science in 2018 and learned more about the chemistry of marine CDR, his opinion changed. Now he’s the executive director of the nonprofit Carbon to Sea Initiative, one of the largest private funders in the space. “My entire focus for the last 6 years or so has been building the philanthropic response for marine CDR,” he says.

“We have made approximately $30 million in grants to universities, research institutes, and start-ups around the world,” Gagern says. To this end, they’ve provided funds to the LOC-NESS project, the OAEPIIP project, and [C]Worthy, among others.

Not only does the Carbon to Sea Initiative fund research, but the nonprofit also brings the research community together by hosting annual science meetings. “The future for us is going to be really focused on continuing building consensus on viability and desirability of OAE,” Gagern says.