Why using the oceans to suck up CO2 might not be as easy as hoped

Why using the oceans to suck up CO2 might not be as easy as hoped

One idea that is gaining attention and investment is to add minerals to the oceans that could trap carbon dissolved in them.

However a study published last week in Frontiers in Climate shows that there are limitations to one promising strategy. It relies on an olivine volcanic mineral. The theory is that seawater could be alkalized by adding ground up olivine. This helps convert carbon dioxide from the atmosphere into a stable form and allows oceans to absorb more carbon dioxide.

Researchers at the GEOMAR Helmholtz Centre for Ocean Research in Germany recently dissolved fine-grained sand made up primarily of olivine in artificial seawater. Over a period of 134 days, they found, the water’s alkalinity actually decreased. According to the researchers, this and other factors decreased the amount of carbon that was removed by five times compared to olivine’s theoretical potential.

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Another study found that dissolving Olivine in seawater filtered or artificially filtered produced a lower increase in alkalinity than was expected. Still another recent preprint paper found similarly confounding results for other minerals that had been expected to boost ocean alkalinity.

However, other studies have raised concerns about an alternative ocean-based approach: growing and sinking it in order to absorb and store carbon.

It will be crucial to find viable ways to reduce greenhouse gas emissions in the next decades. A National Academies report in December on ocean-based carbon removal noted that the world may need to suck up an additional 10 billion tons annually by midcentury to limit warming to 2 @C.

Boosting ocean alkalinity could theoretically remove tens of billions of tons each year on its own, according to the research group Ocean Visions. However, the National Academies panel pointed out that it will require shipping, grinding and extracting rocks at roughly the same scales. All of these would have significant environmental consequences.

The new studies have not yet provided the definitive answer as to whether any of these methods are feasible in reaching carbon removal targets. But Michael Fuhr, a doctoral student at GEOMAR and one of the authors, said that their results suggest that this approach may not be as feasible as previously thought. He also stated that it may only work in certain areas where the ocean chemistry allows. This could be areas with low salinity, but high levels of organic sediments that will increase acidity. Fuhr and others believe that more fieldwork and lab experiments will be required to determine if this method works in real life, what the ideal conditions, and if other materials are better. Maria-Elena Vorrath from the Alfred Wegener Institute for Polar and Marine Research said in an email that the study showed that the olivine process does not work as we thought. But she stressed that the mineral remains “one of the most permanent and promising methods nature gives us.”

“We just need to understand and read the manual,” she wrote, noting that water mixing and other variables in the actual oceans could alter results seen in the lab.

One company, Project Vesta, has been planning to conduct a field trial in the Caribbean for several years, which would entail spreading olivine sand along beaches or in shallow waters. Tom Green, chief executive officer of the company, said that the company has also been conducting toxicology testing and carrying out laboratory experiments.

Project Vesta began as a nonprofit but is now a so-called public benefits corporation, which means it has the twin goals of making a profit and achieving social good. Green states that the goal is to eventually sell carbon credits for any greenhouse gases removed with olivine.

A handful of additional startups are working on other ways of boosting ocean alkalinity, through approaches including electrochemical processes. Those include Ebb Carbon, Planetary Technologies, and Seachange, all of which have pre-sold tons of carbon removal they expect to achieve to companies including Shopify and Stripe.

Meanwhile, the National Academies panel called for setting up a $125 million US research program to study whether we could develop ways to scale up or accelerate these processes, identify environmental side effects, and figure out how to reliably measure and verify whether carbon removal is occurring.

“Ocean Geochemistry is complex,” says Wil Burns, a Northwestern University visiting professor who studies carbon removal. “We’re going to need to do a lot of iterations of this research, under very different conditions and different scales, to draw conclusions that we could do these at large scales and monetize them.”

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