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.

Antacid treatment

In 2014, Rebecca Albright, an expert on corals at the time with the Carnegie Institution, worked with colleagues to mix seawater and sodium hydroxide in a tank and then release the solution into the wild in the Great Barrier Reef.

“After mixing, we pumped the [treated] water onto the reef flat and let it traverse the reef flat naturally, bathing the reef with alkaline water, and we measured the calcification response,” said Albright, now with the California Academy of Sciences. “We used a dye tracer to be able to differentiate the treatment water from the ambient seawater.”

The researchers were not trying to test OAE, but to prove once and for all that ocean acidification was a major reason behind coral decline. Their research showed that when they returned the seawater’s chemistry to a more alkaline state — similar to that of the preindustrial past — the coral reefs began to calcify more quickly. In other words, ocean acidification was indeed a culprit.

Ocean acidification happens when seawater absorbs excess CO2 from the atmosphere. Since the Industrial Revolution, ocean acidity has jumped by 30%, making life more difficult for many marine organisms. It has damaged not only coral reefs but oysters and clams as well. Scientists are also concerned about pteropods (free-swimming sea snails and slugs) and some types of phytoplankton as acidity grows. Declines in these species would impact animals higher up the food web.

Jeremy Hance, Mongabay, 25 January 2023. Full article.

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