Harnessing the Ocean to Combat Climate Change

Scientists say it may not be enough to switch to renewable energy, drive electric vehicles and move to low-carbon manufacturing to avoid the most dangerous impacts of climate change. To meet international climate goals, it’s also necessary to remove 10 gigatons of atmospheric CO2 every year between now and 2050, according to a 2019 report by the National Academy of Sciences, Engineering, and Medicine.

Some strategies are already under way, such as technologies aimed at sucking carbon dioxide directly from the air, agricultural techniques for storing carbon in soils, and changes in how forests are managed. Now, some researchers are looking at how the ocean could soak up additional carbon–and what the benefits and risks would be.

“We seriously need to figure out how to remove some CO2, and it’s already becoming pretty clear that you can’t do it all on land,” says David Keller, a senior scientist at the Geomar Helmholtz Centre for Ocean Research Kiel in Germany. “The ocean plays a major role in the carbon cycle, and that’s where most of the carbon is stored anyway. I think it just makes natural sense to look there. Of course, we don’t want to mess up the ocean.”

Ideas for ocean-aided carbon removal include dumping tons of iron filings in the ocean as a nutrient to promote plankton growth–something that has been done more than a dozen times on a small scale. Other proposals involve building huge offshore kelp farms or restoring coastal ecosystems.

Whether such techniques can be effective and safe, especially on a large scale, remains to be seen. Scientists and entrepreneurs say ocean carbon removal needs more research as well as a sustainable economic model.

Tinkering with the ocean could face hurdles in gaining acceptance from the public and people who depend on the sea for their livelihoods, says Holly Jean Buck, an assistant professor of environment and sustainability at the State University of New York at Buffalo and author of “After Geoengineering: Climate Tragedy, Repair and Restoration.” Still, it’s an important option to consider, she says. “We already know what can slow down emissions. But in terms of removing emissions, we just don’t have a lot out there.”

Experts convened in 2021 by the National Academies of Science, Engineering and Medicine identified six ocean carbon removal technologies that might make a dent in atmospheric carbon dioxide. The report recommended a $125 million research program to better understand the challenges, including potential economic and social effects, and estimated it would take $1.3 billion to translate these ideas into scalable demonstration projects. No dedicated program has been formed, although some philanthropic groups are pledging small amounts to support research.

Meanwhile, some green entrepreneurs have already been testing their own ideas for employing the ocean to remove carbon. Here’s a sampling:

Ocean Antacids

San Francisco-based Project Vesta says it is readying an experiment on a Caribbean island later this year to add a carbon-absorbing mineral to seawater to act as a kind of massive antacid tablet. Boosting alkalinity causes a series of chemical reactions that convert dissolved CO2 in the seawater into stable bicarbonate and carbonate molecules, which in turn causes the ocean to absorb more CO2 from the air.

The nonprofit firm plans to grind a volcanic green mineral called olivine into sand-like particles and spread it along the beach of a cove on the island, which it declined to name. As waves and currents dissolve the olivine, it is expected to create a series of chemical reactions that allow the ocean to capture CO2 from the air. A second bay on the island without the olivine sand will serve as a control site. “We do change the ocean chemistry, but we do it in a very gradual way,” Project Vesta CEO Tom Green says.

Meanwhile, Canadian startup Planetary Technologies plans to use nickel-mine waste, or tailings, to make an alkaline material that can be added to the ocean. The tailings are used in a process with electrical current to split water into hydrogen and oxygen and produce a byproduct called mineral hydroxide. Added to seawater, the hydroxide raises the alkalinity and captures more CO2 from the air, the firm says. The idea is to add the compound to existing industrial outfalls that lead to the ocean.

“We start at the mine site, produce our very mild pure form of alkalinity, and then we transport that to the coast and enter that into seawater through a permanent outfall,” says Planetary Technologies CEO Mike Kelland. The startup expects to have its pilot plant running by the end of 2024 near a mine in Quebec.

Researchers led by Geomar devised an experiment using large clear cylinders to measure how adding various alkaline minerals to seawater helps reduce CO2. The first phase took place off the coast of Grand Canary Island in September and October. The second part is planned for May in a Norwegian fjord. Early results show the ocean chemistry must be carefully monitored to make sure the carbon is properly absorbed. If the alkalinity gets too high, a chemical precipitate forms which can be toxic to ocean plankton.

Aquaculture startup Running Tide proposes a flotilla of basketball-size buoys that support fronds of the macroalgae kelp underneath—in what it calls “kelp microforests.” As the kelp grows, it would absorb CO2 from the ocean. Once the kelp plant gets too big and heavy, it would sink to the bottom, dragging with it the carbon it has absorbed.

Help From Kelp?

As an idea for boosting capture of C02, aquaculture startup Running Tide proposes creating what it calls ‘kelp microforests.’ Here’s how the system would work:

Flotillas of basketball-size, biodegradable buoys would support kelp fronds underneath. As the ocean draws C02 from the atmosphere, the kelp would absorb it from the water ​during photosynthesis​.

Once a kelp plant gets too big and heavy, it would sink, dragging with it the carbon it has absorbed. Eventually it would be buried in sediments or consumed by deep-sea marine life, Running Tide says.

Flotillas of basketball-size, biodegradable buoys would support kelp fronds underneath. As the ocean draws C02 from the atmosphere, the kelp would absorb it from the water ​during photosynthesis​.

Once a kelp plant gets too big and heavy, it would sink, dragging with it the carbon it has absorbed. Eventually it would be buried in sediments or consumed by deep-sea marine life, Running Tide says.

Flotillas of basketball-size, biodegradable buoys would support kelp fronds underneath. As the ocean draws C02 from the atmosphere, the kelp would absorb it from the water ​during photosynthesis​.

Once a kelp plant gets too big and heavy, it would sink, dragging with it the carbon it has absorbed. Eventually it would be buried in sediments or consumed by deep-sea marine life, Running Tide says.

Flotillas of basketball-size, biodegradable buoys would support kelp fronds underneath. As the ocean draws C02 from the atmosphere, the kelp would absorb it from the water ​during photosynthesis​.

Once a kelp plant gets too big and heavy, it would sink, dragging with it the carbon it has absorbed. Eventually it would be buried in sediments or consumed by deep-sea marine life, Running Tide says.

“It just hits the mud and then some of it gets eaten, becomes part of the ecosystem down there,” says Running Tide CEO Marty Odlin, a former commercial fisherman who has an engineering degree from Dartmouth. “The carbon just becomes part of what’s called the deep-ocean conveyor belt, gets dragged along the bottom of the ocean and pops up at some upwelling site 800 to 1,000 years from now.”

Mr. Odlin and Running Tide’s academic partners are figuring out where to best to place the buoys to take up the most CO2. They are also considering using different species of macroalgae depending on the location. Its pilot plant in Portland, Maine, is under construction.

The recent National Academies study notes that too much decomposing kelp on the seafloor could cause “dead zones” of low-oxygen water that could harm marine life, while too much floating kelp could rob the surface layer of nutrients that supply other marine organisms.

Carbon Burial at Sea

What if you could grab CO2 from the air and bury it in the volcanic rock beneath the seafloor? That’s the idea behind Solid Carbon, a Victoria, B.C.-based consortium that includes U.S. and Canadian scientists.

Floating ocean platforms equipped with direct air capture machines, like one operating now in Iceland, would pipe the CO2 gas into basalt formations that lie 350 feet below the seafloor. The basalt would absorb the carbon dioxide and turn it into rock.

Solid Carbon plans a demonstration project in 2024 at Cascadia Basin, a volcanic region about 130 miles off the coast of British Columbia. Kay Moran, project leader and CEO of Ocean Networks Canada, an academic consortium that operates undersea observatories, says the basin could hold the equivalent of 15 years of global human carbon emissions.

Marine experts warn that any buried CO2 needs to be monitored to make sure it doesn’t escape from the formation and bubble up into the ocean.

Six Avenues for Ocean Capture

The National Academies identified six promising methods for ocean carbon capture, and recommended a budget to get the projects into field trials or a pilot stage, and to study potential side effects on marine life:

Nutrient fertilization: Add nutrients such as nitrogen, iron or phosphorus to stimulate production of marine phytoplankton and enhance uptake of CO2 through photosynthesis. $290 million

Artificial upwelling and downwelling: Use pipes and pumps to bring up deep, cold nutrient-rich water to increase phytoplankton production at the surface to capture CO2 from the atmosphere, and bring down surface water to take that carbon into the deep ocean. The study notes it could be difficult to ensure the carbon remains locked up and doesn’t return to the ecosystem. $25 million.

Seaweed cultivation: Create large-scale seaweed farms that transport carbon to the deep ocean or into sediments. $130 million.

Recovery of ocean and coastal ecosystems: Replant and restore ocean ecosystems to kick-start carbon absorption by marine animal and plant life. $220 million

Ocean-alkalinity enhancement: Increase ocean alkalinity with minerals and other additives to allow it to safely absorb more CO2. $125 million to $200 million.

Electrochemical approaches: Use electric current in processes including increasing alkalinity of seawater to capture CO2. $350 million.