Terrestrial carbon sequestration — trees, soils, wood vaults, biochar — has been hot in the carbon removal world for the past few years. There have been dozens of investigations into the legitimacy of forest sequestration claims, money from big food companies pouring into figuring out how farmers can use their crop land to pull more carbon into the soil and a humming ecosystem of startups, marketplaces and financing for terrestrial-based projects and credits.
But the carbon economy is missing a huge percentage of possible sequestration potential, 71 percent to be exact — the percentage of the Earth that is covered by oceans. The ocean is actually our biggest carbon sink on the planet. It stores 50 times more carbon than the atmosphere, and 20 times more than terrestrial plants and soils. And it has already been a giant help mitigating climate disaster by absorbing 30 percent of the carbon dioxide caused by human activities.
But the ocean is also bearing the brunt of CO2 damage.
“An incredible amount of heat being driven into the ocean, and the excess CO2 that we’re putting into the upper layer of the ocean is causing acidification,” said Ocean Visions CEO Brad Ack. “Those two stressors are by far the biggest threats to the ocean. Much bigger than plastics and overfishing.”
Ocean Visions sits in the middle of a network of ocean-focused organizations including Scripps Institution of Oceanography, the Woods Hole Oceanographic institution at Stanford and the Monterey Bay Aquarium. Together they help move research ideas into prototypes and business models.
And yet ocean sequestration is still behind on investment and maturity compared with its terrestrial counterpart. But that is starting to shift. Earlier this month, Microsoft announced a two-year agreement with Running Tide, a startup focused on ocean sequestration, to remove 12,000 tons of carbon through its ocean-supported technology. In 2022, Brilliant Planet, a company using algae blooms to pull carbon out of the air and into the ocean, announced a $12 million funding close.
Here are three technologies that could bolster the ocean’s sequestration potential and the main players in each space.
1. Microalgae cultivation
Microalgae cultivation is basically the ocean equivalent of planting more trees to suck up more carbon. Microalgae are one of the most dominant organisms on the planet and they grow, multiply and replicate very rapidly.
“The sheer amount of space that could potentially be used to increase the amount of microalgae in the ocean offers a really interesting possible pathway for sequestering more carbon,” said Ack.
Brilliant Planet is a startup mimicking the natural ocean’s microalgae carbon cycle on land to permanently sequester the carbon. It replicates algae blooms at facilities in coastal desert areas where there is little natural growth, such as in Morocco and South Africa.
By adding nutrients to this underproductive ocean ecosystem, the algae can proliferate, pull carbon out of the air via photosystems and then hopefully end up at the bottom of the ocean as deep blue carbon — a very stable form of sequestration.
“The question is, how much of that microalgae actually ends up in that deep blue carbon pool?” Ack said. “And the jury’s still out on that question.”
2. Seaweed sinking
Seaweed is one the fastest growing plants on the planet and requires very little inputs — and none that aren’t natural. But seaweed does need something to attach to, which limits where in the ocean it can grow.
“We already grow seaweed at very large scales around the world, mostly in Asia,” Ack said, “But we do in inland waters that are easy to access by small boats and farmers. The question is, can you take this technology and do it offshore in the open ocean at very large scales?”
And it has seen more investment in the past few weeks than other ocean technologies.
Once the seaweed has grown, it would need to be harvested, compressed and/or sunk to the bottom of the ocean, where it is stored in very low oxygen conditions so it can’t biodegrade.
Running Tide has engineered a buoy system for just this process. According to Brad Rochlin, director of strategic partnerships at the startup, it uses about 40 metric tons of tree clippings compressed into pucks as the attachment points for the seaweed. They are also coated with limestone and seeded with seaweed to then float out to sea to grow the seaweed for a few weeks or months and let the limestone dissolve to combat ocean acidity. And then at some point the buoyancy flips, and the buoy sinks to the bottom for storage.
The company has been working out of an area near Iceland and is deliberating locations for the buoys to encourage the most carbon-stable sequestration once it sinks — about 1,000 meters is ideal.
One interesting wrinkle Running Tide is having to contend with is the permitting system in all countries. There are only dumping permits for commercial ocean activities — nothing that addresses putting something into the ocean that could actually heal it. So Running Tide has been working with the Icelandic government to create these new permit types.
“It’s a research permit, in the sense of we have to share a lot of that information back, which we want to do anyways,” said Running Tide CEO Marty Odlin. “So it’s interesting in between where it is a business activity, but the ability to do it is contingent on you sort of understanding the ocean better and in a way that provides value to the academic scientific community.”
3. Enhancing sequestration with electrochemistry
A slightly different tactic to tap into the ocean’s sequestration potential revolves around a chemical reaction in the water instead of photosystems in plants. Using renewable energy-powered electrodialysis, the ocean water is split into an acid and an alkaline base. The alkaline base is added back to the ocean to counteract the surface of the ocean’s acidification and allow it to absorb more CO2 from the atmosphere. The acid filled with CO2 is captured and stored for sequestration.
Spun off from CalTech, Captura is a big player in this space and won an Xprize in 2022, gaining $1 million in funding as a reward.
