How oceans could be used for carbon capture on a big scale

Carbon capture from smokestacks or the air, using technology and tree planting, has received a lot of attention and funding. But last week, a few hundred scientists around the world argued that more attention should be paid to carbon capture in the ocean.

“The ocean’s carbon content is 50 times larger than what is in the atmosphere. Its sheer size also means that ocean-based climate solutions can be scaled to significantly mitigate climate risk,” they wrote in a letter posted on the web page of Ocean Visions, a non-profit umbrella group for universities and oceanographic institutions focused on ocean-climate restoration solutions.

The problem? Even scientists know little about the effectiveness, risks or impacts of ocean carbon capture solutions.

Kate Moran, president and CEO of Ocean Networks Canada and a spokesperson for the scientists who wrote the letter, said more information is crucial for making policy decisions about ocean carbon capture.

“We do need to, as a collective community, get behind research needed to understand these issues, and it’s pretty urgent,” she said in an interview from the Canadian Coast Guard ship Tully off the coast of B.C., where she is doing some of that research.

The letter was signed by a number of scientists from the Canadian firm Planetary Technologies, including its chief ocean scientist, Will Burt. Planetary Technologies ran its first ocean tests of its carbon capture technology in Halifax harbour this week (see photo above).

Burt hopes the letter helps the public “build some confidence that what we’re doing is … widely believed scientifically to be worth exploring.”

By now, you might be asking, “OK, but what kinds of solutions are we even talking about?”

They fall into two main categories: biotic and abiotic.

Biotic ocean carbon removal is similar to planting trees on land to absorb CO2, except it involves marine or coastal ecosystems and plants. The carbon they store is called blue carbon, and it can involve:

Seaweed or “macroalgae” such as kelp. The carbon can later be sequestered — for example, by sinking it to the ocean floor. (That’s one of the solutions Moran was researching on the Tully last week.)

Ocean alkalinity enhancement. This is being tested by Planetary Technologies. It involves adding “antacids” made of rock dust, such as magnesium hydroxide, to the ocean to neutralize dissolved CO2. This converts the CO2 into stable minerals and salts, effectively removing it from the carbon cycle. Like a sponge that’s been squeezed out, the water regains the capacity to absorb more CO2 from the atmosphere. In the photo above, you can see Planetary Technologies’ researchers taking measurements from a boat after the antacid was added to the water, along with a red dye that helps track how the antacid spreads. Burt says this technology should also reverse ocean acidification that harms coral reefs and shellfish.

Ocean carbon capture “could be a really key player.”

— Emily Chung