A pteropod shell is shown dissolving over time in seawater with a lower pH. When carbon dioxide is absorbed by the ocean from the atmosphere, the chemistry of the seawater changes and the ocean becomes more acidic. Image by NOAA.

World - Re-carbonizing the sea: Scientists to start testing a big ocean carbon idea

Ocean alkalinity enhancement (OAE) involves releasing certain minerals into the ocean, sparking a chemical reaction that enables the seawater to trap more CO₂ from the air and mitigating, albeit temporarily, ocean acidification.

  • Some scientists believe OAE could be a vital tool for drawing down and securely storing some of the excess CO₂ humanity has added to the atmosphere that is now fueling climate change.
  • Yet many questions about OAE remain, including most prominently how it would impact marine life and ecosystems.
  • Several programs are aiming to spark the research needed to answer these questions, including field tests in the ocean.

Imagine showers of little green sand grains drifting through the ocean: collecting on coral reefs, rolling off the backs of whales, sprinkling schools of tuna — and helping to save all those creatures, and humanity, too. At least that’s the idea.

These green showers are crushed olivine, an abundant volcanic mineral, delivered by a fleet of ships. And it is climate change that launched these thousand ships, crisscrossing the ocean in a surreal bid to undo the damage we’ve done. You see, as the olivine settles on the ocean floor it disintegrates and chemically transforms, making that part of the ocean a little more alkaline and converting dissolved CO2 into carbonate and bicarbonate molecules, a process that stores the carbon for hundreds of thousands of years. The seawater can then trap more CO2 from the air to replace the stored carbon.

Scientists call this ocean alkalinity enhancement, or OAE, and some believe it could be a vital tool for drawing down and securely storing a portion of the 1.5 trillion tons of CO2 that we’ve added to the atmosphere since the industrial revolution, not to mention the billions more we’ll add before we hit net zero.

“Ocean alkalinity enhancements show some outsized promise” in terms of potential cost and permanence of locking away the CO2 compared to other carbon sequestration ideas, said David Koweek, science director at the U.S.-based NGO Ocean Visions.

Moreover, OAE has an additional potential boon mitigating, albeit temporarily, another impact of our fossil fuel addiction: ocean acidification.

Of course, the prospect of dumping boatloads of crushed minerals across the ocean raises some concerns. Researchers like Koweek wonder how it would impact marine life and ecosystems. So they say we need much more research on this idea, including field tests in the ocean.

That research is coming soon, in a big way.

Koweek and Ocean Visions have been evaluating OAE grant proposals in partnership with the Palo Alto California-based NGO Additional Ventures. Co-founded by a former Meta executive, Mike Schroepfer, Additional Ventures has put aside $100 million for OAE research and development. The two NGOs are currently evaluating proposals for two different grants. The first will support projects to develop prototypes of equipment to produce or deliver minerals, with funding ranging from $750,000 to $1.5 million; the second will support projects to explore how OAE could be done safely and effectively, with minimum funding of $10 million. They’ll announce the grant recipients later this year and research will take up to five years.

The U.S. government is also accepting grant applications for researching various methods to remove carbon dioxide and mitigate acidification in marine areas, under NOAA’s Ocean Acidification Program.

The carbon dilemma

The Earth’s global ocean is an unparalleled carbon storehouse. Covering 70.8% of the world’s surface, the ocean stores around 50 times more carbon than the atmosphere and about 20 times more carbon than every plant and plot of soil on land combined. For this reason alone, many scientists are looking to the ocean as a tool against climate change.

The Sixth Report from the IPCC, released in April 2022, found that CO2 removal will be “unavoidable” because some emissions will be “hard to abate” in report-speak — think airplanes. This followed a 2019 report by the National Academies of Sciences, Engineering and Medicine (NASEM) showing that carbon sequestration tools will need to take in around 10 gigatons of CO2 annually by 2050 — more than a quarter of today’s annual emissions.

Some carbon sequestration methods are already in use: reforestation, agroforestry, restoring peatlands and changing agriculture to improve CO2 sequestration in soil. In the ocean, communities are beginning to restore kelp forests, mangroves and other blue carbon powerhouses. And interest is rising in other methods, such as direct air capture and OAE.

None of this negates the need to cut emissions aggressively. Instead, the IPCC is saying we will need to do both: slash emissions and dramatically upscale tools to sequester carbon.

OAE is especially attractive since it mimics nature — only on a faster timescale.

“If we did nothing about the climate problem at all, Earth would rebalance its carbon cycle on the scale of tens to hundreds of thousands of years by weathering silicate minerals on land, and sending that carbon into the ocean in the form of alkalinity,” said Koweek. “And so, ocean alkalinity enhancement is an acceleration of a natural cycle.”

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