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Practical Magic

A sea change for carbon capture

How much more CO2 can the ocean swallow, without harming sensitive ecosystems?

Rendering of a large-scale Captura facility that captures carbon dioxide from ocean water.

Rendering of a large-scale Captura facility that captures carbon dioxide from ocean water. Courtesy of Captura

There are many things we don’t know about the ocean, the most unexplored part of Earth, but there are two things we do know: Water covers almost 70 percent of the planet, and the ocean is 96 percent plus of that. And the ocean absorbs about 30 percent of atmospheric carbon dioxide, a feat for which it doesn’t receive much credit.

How much more CO2 can the ocean swallow, without harming sensitive ecosystems and further accelerating the acidification endangering coral reefs, mollusks and other sea life? A school of early-stage entrepreneurs is fishing for answers, through both technological and biological means. 

In mid-January, Los Angeles-based Captura — headed by well-known carbontech industry executive Steve Oldham, former CEO of direct air capture firm Carbon Engineering — raised $12 million in Series A financing for its proposed solution, which it calls direct ocean capture. The round was led by the venture arm of oil company Equinor, and also includes backing from Aramco Ventures, the California Institute of Technology (a.k.a. Caltech), Future Planet Capital, Hitachi Ventures and mTerra Ventures.

Yes, this is a relatively small round in the scheme of climate tech venture moolah, but Captura is notable for other reasons. It was a milestone winner last spring in the massive Carbon XPrize fronted by Elon Musk, along with roughly a dozen of the other competitors, plucked from the field of close to 300 companies angling for the money. Captura has also captured the attention of Frontier, a collaboration coordinated by Alphabet, Meta, McKinsey, Shopify and Stripe that has committed $925 million to purchase carbon removal from promising approaches. Frontier has signed a $500,000 prepurchase relationship with Captura to capture 508 tons of CO2, with the option for a long-term offtake deal in the future, if the technology delivers on certain pilot project metrics.

Captura’s approach uses electrochemistry to absorb CO2 from ocean water and then return the CO2-depleted water back into circulation, using renewable energy to power the process, Oldham told me. That decarbonized water is then available to absorb more CO2, and the process is repeated — kind of like dialysis on a human patient.

"Our approach is fundamentally different," Oldham said. "We don’t add anything to the ocean, and we don’t take anything from the ocean." That is, except for the captured CO2, which Oldham said can be used for feedstock by other companies, such as synthetic fuels companies (think Lanzatech, although there’s no official deal there), or sequestered at a storage site. The company is working with nonprofit Ocean Visions and recently hired an oceanographer, who will be responsible for making sure Captura’s technology is as safe for ocean ecosystems as its executives like to claim.

Oldham’s interest in the ocean as a carbon capture frontier is informed by his background with land-based options, which he notes require massive amounts of capital, energy and space. "The ocean is proven, it’s enormous, and it’s free."

He touts Captura’s ability to use existing offshore infrastructure for its systems, such as desalination plants or oil rigs — and especially in locations where there are existing carbon sequestration and storage options. Its pilot site, off Newport Beach, California, is capable of slurping up 1 metric ton of CO2 annually. The next-generation site under construction with the aforementioned financial support will be capable of capturing 100 times that capacity. The cost for removing the CO2 will be "well under" the $100-per-ton price point that the Department of Energy is encouraging with its grant funding. (Did I mention Captura also has DOE backing?)

Captura's pilot facility at Newport Beach, California

Captura's pilot facility at Newport Beach, California. Courtesy of Captura

While Captura’s business models are still under development, the startup is exploring scenarios in which it would license its system to organizations with construction and development experience, Oldham said.

Joanna Klitzke, procurement and ecosystem strategy lead with Frontier, said one big part of the ocean’s appeal as a carbon capture frontier is the fact that it doesn’t require the use of arable land — making it more potentially scalable. Part of Frontier’s specific interest in Captura stems from its interest in simultaneously addressing ocean acidification — by removing CO2 to more natural levels. "We need a diversity of shots on goal," Klitzke said when we chatted about the interest in Captura.

The tide is turning

Captura’s electrochemical approach represents one of six early-stage approaches to ocean carbon removal outlined in a recent report from World Resources Institute, ranging from abiotic methods (those that rely on the ocean’s physical or chemical properties to remove CO2) to biotic techniques (those that depend on photosynthesizing organisms to get the job done). Here are six early approaches that have WRI’s particular attention: 

  • Electrochemical removal 
  • Alkalinity enhancement 
  • Artificial downwelling 
  • Nutrient fertilization
  • Artificial upwelling
  • Seaweed cultivation

The WRI report mentions coastal wetland restoration but I've excluded it from the list above because it's at a more mature stage of development. Ocean Visions, a technical adviser to XPrize for the ocean capture entrants, explains the theory behind many of these methods at this resource

So, aside from Captura, what other early-stage companies are making waves and capturing funding? Here are a few that the GreenBiz crew is watching:

  • Vesta: It’s experimenting with applying olivine to coastlines, accelerating sequestration. The company is one of the new climate tech firms in Elemental Excelerator’s latest portfolio, disclosed in November. 
  • Planetary Tech: The firm calls its technology an "antacid" for the ocean, and it’s another of the XPrize milestone winners, backed with about $6.1 million when I last wrote about them in April.
  • Running Tide: Started as an oyster farm, the company hopes to grow kelp and sequester carbon by harvesting it and sinking it to the ocean floor. It was among the earliest companies generating buzz, but more recently the scientific community has raised concerns about its potential impact on ocean ecosystems.
  • Ocean-based Climate Solutions: The company is developing a wave energy-powered system called Ocean Surface Carbon Relocation that pumps carbon-saturated water from the surface down 400 to 500 meters and pulling up cool water and phytoplankton from those depths. (So, combined downwelling and upwelling.) The idea is to sequester CO2 while restoring local ecosystems. CEO Phil Kithil told me the company is planning its next trial off the California coast in the spring.
  • Lillianah Technologies: Technical founder Benjamin Slotnick, a geologist with expertise in the carbon cycle, is working on this stealth startup’s plan to optimize the ocean’s existing biological pump for managing CO2 sequestration using microalgae, including phytoplankton. Stay tuned for more details on the approach in a future article.

As with everything related to the ocean, we must tread lightly to ensure that any engineered approaches don’t tip the balance of marine ecosystems. What ocean carbon capture startups deserve our attention? Alert me at

Editor's note: This story was updated Feb. 1 to correct the name for Ocean-based Climate Solutions. 

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