Ocean geoengineering research has found no evidence of harm to marine life

Can we safely remove carbon dioxide from the atmosphere by counteracting ocean acidification? Perhaps, suggests an experiment in which ships poured 65,000 liters of caustic soda into the Gulf of Maine off the US East Coast in August 2025.

“We are the first group to do a shipboard experiment with increasing alkalinity,” he says Adam Subhas at the Woods Hole Oceanographic Institution in Massachusetts, whose team announced their first findings at the conference Ocean Sciences Meeting in Glasgow, UK on 25. “We can definitely say that additional CO2 absorption has occurred as a result of this experiment.”

Subhas says that 2 to 10 tons of CO2 were removed from the atmosphere over the next four days, and the team estimates that up to 50 tons could be removed in total. Additionally, no significant effect on marine life was observed.

However, when he asked The new scientistSubhas acknowledged that the team still needs to estimate the emissions needed to produce the sodium hydroxide and transport it to the test site. This means that it is not clear whether the experiment resulted in a net removal of CO2.

“That’s a really good question,” said Subhas. “That’s going to be a really critical area of ​​research moving forward.”

The oceans store 40 times more carbon than the atmosphere and have absorbed more than a quarter of the excess CO2 we pumped into the atmosphere. This excess CO2 reacts with water to form carbonic acid, which means the oceans are becoming more acidic.

Ocean acidification could have a major impact on many marine organisms, for example by dissolving their carbonate shells. It also reduces the ability of the seas to absorb more CO2.

Scientists are investigating a number of methods to counter ocean acidification, including adding magnesium hydroxide to sewage that flows into the ocean, adding ground olivine to the coast, and pumping seawater through land-based treatment plants. Some companies already sell carbon credits based on increases in alkalinity.

“This is something that the private sector is moving forward with right now,” says Subhas, which is why non-commercial tests like the one his team conducted are needed.

Because of the controversial nature of these kinds of trials, the team began by involving local people, particularly in the fishing community, a team member says Kristin Kleisner from the Environmental Defense Fund, a nonprofit organization based in New York. “Two-way dialogue is really critical,” he says.

The experiment itself involved three ships and was monitored in several different ways, from satellites to floating sensors to ocean gliders that zigzag up and down. The sodium hydroxide was mixed with a trace amount of a dye called rhodamine to accurately monitor its dispersion.

The team measured concentrations of microbes, plankton, fish larvae and lobster larvae, as well as levels of photosynthetic activity, he says Rachel Davitt at Rutgers University in New Jersey. “Our field trial had no significant impact on the biological community,” he says.

The extra carbon absorbed by the ocean due to increased alkalinity is converted into bicarbonate ions, or dissolved baking soda, Subhas says. “We expect this carbon to be locked away for tens of thousands of years. It’s one of the most persistent forms of carbon removal.”

The nature of the process means the CO2 is removed and stored in a single step, says Subhas. This is an advantage over some other approaches where CO2 is first removed from the atmosphere and then must be permanently stored in some form.

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