Researchers at the GEOMAR Helmholtz Center for Ocean Research in Germany recently dissolved fine-grained sand consisting mainly of olivine in artificial seawater. Over a period of 134 days, they found that the alkalinity of the water actually decreased. These and other factors reduced the amount of carbon removed by a factor of five compared to olivine’s theoretical potential, the researchers said.
Other research groups also recently found that dissolving olivine in filtered and artificial seawater caused less of an increase in alkalinity than expected, the study said. Another recent one preprinted paper found similarly confusing results for other minerals expected to increase ocean alkalinity.
Meanwhile, several additional studies recently have cast doubt on another ocean-based approach: growing seaweed and sinking it to suck up and store carbon.
Finding viable ways to reduce greenhouse gases will be critical in the coming decades. A National Academies report in December on ocean carbon removal noted that the world may need to imbibe another 10 billion tons per year by mid-century to limit warming to 2°C.
Increasing the ocean’s alkalinity could theoretically remove tens of billions of tons per year on its own. according to the Ocean Visions research group. But the National Academies panel noted the need to extract, grind and ship rocks at roughly similar scales, all of which would also have significant environmental impacts.
The new studies haven’t provided the final, definitive word on whether any of these methods are viable ways to achieve those carbon removal goals.
But Michael Fuhr, one of the authors of the olivine study and a doctoral student at GEOMAR, says their findings suggest that this approach is “not as straightforward as previously expected.” He adds that it can only work well in certain places where the ocean chemistry is good. These could be areas where the water has a low salinity but is rich in organic sediments, which will increase the acidity.
Fuhr and others say additional lab experiments and fieldwork will be needed to determine how well this method works in the real world, what the ideal conditions are, and whether other materials hold more promise.
Maria-Elena Vorrath, a researcher at the Alfred Wegener Institute for Polar and Marine Research, said in an email that the research shows that the olivine process isn’t working the way 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 mixing water and other variables in the actual oceans can alter the results in the lab.
A company, Project Vesta, has been planning a field trial for several years in the Caribbean, scattering olivine sand along beaches or in shallow waters. It has also conducted lab experiments, toxicology tests and planned field trials on the US East Coast, said Tom Green, the company’s CEO.
Project Vesta started out as a non-profit but is now a so-called public benefit organization meaning it has the dual goals of making a profit and achieving social welfare. The hope is to eventually sell carbon credits for every greenhouse gas removed with olivine, Green says.