A group of scientists from the Woods Hole Oceanographic Institution (WHOI) is planning to release 6,600 gallons of sodium hydroxide into the waters south of Martha’s Vineyard in September to gauge its ability to improve the ocean’s capacity to absorb carbon dioxide from the atmosphere.

The field test is the first of its kind in the U.S. and is meant to validate laboratory experiments indicating that ocean alkalinity enhancement, or OAE, could reduce atmospheric carbon dioxide and thus global warming while having little effect on the local environment.

If the September test is successful, the research team plans to perform a second field test next summer about 35 miles north of Provincetown in the Wilkerson Basin, said WHOI associate scientist Adam Subhas, the principal investigator on the project. That experiment would release 66,000 gallons of sodium hydroxide.

The field tests, a type of geoengineering, have provoked some controversy. Fishermen’s groups have argued that a localized increase in ocean alkalinity could affect fish stocks, while other scientists have argued that the environmental impacts will be minor, and the study results could be important in the fight against global warming.

Alkalinity Enhancement

According to the National Oceanic and Atmospheric Administration, even if all human-caused greenhouse gas emissions ended today, the emissions that are already in the atmosphere would continue warming the planet for at least several decades.

That upward trajectory has led to a growing recognition that lowering emissions, while necessary to mitigate the worst effects of climate change, may not be sufficient.

The National Academies of Science, Engineering, and Medicine published a report in 2021 that called for further research into increasing the ocean’s ability to absorb carbon dioxide from the atmosphere to help slow climate change. The report was a key inspiration for the current research project, which is called LOC-NESS, short for “Locking away Ocean Carbon in the Northeast Slope and Shelf,” according to Suzanne Pelisson, director of public relations at WHOI.

The world’s oceans already have sequestered more than half of all the carbon dioxide that humans have released, said the 2021 report, and they likely have the capacity to sequester more. But because dissolved carbon is acidic, it has caused the ocean to become about 30 percent more acidic than in pre-industrial times — eating away at the exoskeletons of coral, lobsters, shrimp, and a wide range of animals with shells.

Deliberately introducing alkaline materials into the ocean could counteract this acidification and improve the ocean’s “buffering capacity,” essentially creating more space for acidic carbon dioxide to continue to dissolve into ocean water. This would allow the ocean to sequester even more carbon without becoming more acidic at the same time.

In-Ocean Experiments

The September experiment will take place about 10 miles south of Martha’s Vineyard and will include both sodium hydroxide and a nonreactive dye so scientists can monitor where the alkaline water flows and track its effects.

Subhas’s team will take baseline measurements before the experiment begins, and an onboard “protected species monitor” will also watch for marine mammals and other protected species to ensure none are present in the study area.

Once initial measurements are taken, the team will dump the sodium hydroxide into the wake of the boat, which will churn the material and the ocean water together while the boat spirals outward, Subhas said. This method, which they tested last fall using only dye, ensures high dilution and evenly distributed alkalinity, Subhas said.

As soon as the sodium hydroxide hits the water, the team will begin taking measurements, Subhas said. Buoys will monitor water quality on the surface, drones will monitor currents, and deep-water rosettes will assess water quality at depth. The team also uses fluorometers and tow nets to measure plankton densities.

“We’re throwing every scientific tool we can think of at this,” Subhas said. The measurements will continue for five days, with scientists working in 12-hour shifts to ensure constant monitoring.

Subhas said that the September experiment is an extremely small-scale version of ocean alkalinity enhancement — the goal is to see if larger experiments are feasible and worthwhile. “We’re doing very small, very controlled experiments,” Subhas said.

The patch of de-acidified seawater is expected to be about 1,600 feet across and about 30 feet deep, and the level of alkalinity should drop to within the Environmental Protection Agency’s acceptable range within one minute of application, Subhas said. The study’s overall impact is like “adding a teaspoon to a bathtub,” he said.

If the experiment demonstrates that ocean alkalinity enhancement improves carbon absorption without negative local effects, Subhas and his team will proceed with the larger experiment next summer.

Diverging Opinions

Subhas said that the experiment’s scientific merit vastly outweighs the potential for harm.

When the EPA invited public comments on its permits for the September study and the one planned for next summer, however, the opinions of commenters varied widely.

The Cape Cod Commercial Fishermen’s Alliance worried that the experiment would cause fish die-offs, either due to the alkalinity itself or the dye. “Alterations to nutrient cycling, ocean circulation patterns, and overall ecosystem functioning could experience unforeseen consequences,” wrote Fishermen’s Alliance policy director Aubrey Ellertson Church.

The Atlantic Offshore Lobstermen’s Association, the New England Fisheries Stewardship Association, and the Mass. Lobstermen’s Association, among others, also expressed concerns for fishery stocks. Nearly all the fisheries groups argued that not enough lab experiments had been undertaken to ensure the safety of the project and called for the permit for the 2025 experiment to be contingent on results from this fall.

Prior lab tests by Subhas’s research team had found the concentrations of sodium hydroxide being deployed should have a negligible effect on microbial ecosystems.

Several scientists who were not affiliated with the research project registered their support for it in comments to the EPA.

Jaime Palter, associate professor of oceanography at the University of Rhode Island, wrote that the experiment’s protocol suggests “extreme safety to sea life.” She also wrote that sodium hydroxide is sometimes used to bolster oyster farms, where it has not appeared to cause damage to sea life.

Morgan Reed Raven, assistant professor of earth science at the University of California Santa Barbara, wrote that the experiment is one of the best ideas yet proposed to help scientists minimize human suffering due to climate change. Supportive comments also came from professors at Yale and the University of California Davis.

Owen Nichols, director of marine fisheries research at the Center for Coastal Studies in Provincetown, said that he thinks much of the concern has to do with communication. Six thousand six hundred gallons “reads like a big number,” Nichols said, adding that, from what he has read of the project, it appears to him that Subhas and his team are “proceeding very cautiously.”

Nichols said it’s important to communicate with the fishing community when doing in-ocean research. “Engaging with the community from the beginning … so it doesn’t come as a shock, I think is really important,” he said.

Subhas said the LOC-NESS team has been meeting with local fishermen “and taking their comments to heart.”

The research team is planning an in-person meeting at Superior Trawl in Narragansett, R.I. on Aug. 14 and is also planning virtual and on-Cape meetings for later in the year.