The olivine treated beach in Southampton, New York. Credit: Chayenne Moreau

In 2022, researchers added crushed green olivine to a beach in Southampton, New York, to test whether the mineral could help the ocean absorb more carbon dioxide. Then they let the waves carry it offshore—and watched what happened to the animals living in the sand.

The results mark the first field evidence for a climate change mitigation idea that, until now, had mostly lived in lab tanks and computer models. Over a year of monitoring, the seafloor community rebounded within months, while nickel, chromium, and other metals linked to olivine did not build up in the animals researchers sampled.

But the trial also revealed how hard it is to judge a technology at the edge of land and sea, where waves bury and uncover the mineral, ordinary beach sand muddies the experiment, and a promising safety signal can still fall short of a green light.

A Rock That Swallows Carbon

Olivine is a greenish mineral common in Earth’s mantle. When exposed to rainwater or seawater, it reacts with dissolved carbon dioxide and helps turn it into bicarbonate, a stable form of carbon that can remain in the ocean for thousands of years.

This process happens naturally, but slowly. Marine enhanced rock weathering tries to speed it up by grinding olivine into sand-sized particles and letting waves do the rest.

Scientists have estimated that spreading crushed silicate rocks on farmland could remove up to 1.1 billion tons of carbon dioxide a year. Some advocates think beaches and shallow seas could accelerate the reaction even more, because waves constantly grind and stir the mineral.

Olivine is a mineral that can absorb its own mass of CO2 when finely powdered. Credit: Aireal

“One ton of olivine sand can take in up to one ton of CO2, depending on the conditions. You just have to spread it out and nature will do its job,” Teresa van Dongen, who created the carbon-capturing materials library Aireal, told Dezeen in 2021.

But olivine can contain trace metals such as nickel and chromium. It may also smother worms, mollusks, and crustaceans living in sand—concerns that have largely been tested in controlled lab studies rather than in the churn of an actual beach.

The Long Island Test

In 2022, the company Vesta placed 650 tons of olivine sand on a beach in Southampton, New York, along with 13,500 tons of ordinary sand used to reinforce the eroding shoreline. Waves carried the olivine offshore.

Researchers sampled sediment before the addition, afterward and again one year later, from the shallows to 160 meters offshore. They compared the olivine area with nearby sites that received only ordinary sand or no sand.

The seafloor community did indeed take a hit, but recovered shortly. Abundance and species richness returned to control levels within about two months, according to the study. Diversity and evenness remained unchanged. One small species, the fringed blood worm, declined significantly in the olivine area, but similar community shifts also appeared where only ordinary sand had been added.

That points to beach nourishment itself as a likely disturbance, rather than olivine alone.

“The natural system is just so dynamic that any dissolving constituents are very rapidly diluted,” Emilia Jankowska of Hourglass Climate, who led the study, told New Scientist.

A Promising Signal Papakōlea Beach, Hawaii, is green mainly because its sand contains abundant olivine crystals. Credit: Vesta

The metal analysis results were also reassuring. Nickel, chromium, cobalt, and manganese stayed comparable across treatments over roughly one year, with no evidence of accumulation in organisms.

Still, critics say the evidence is still limited for now. New Scientist quoted James Kerry of OceanCare as saying the study’s claim of no adverse effects was “stronger than what the evidence shows.” Because researchers sometimes buried olivine under much larger amounts of ordinary sand, animals may have had limited exposure. “The lack of accumulation that’s apparent may reflect limited exposure, not necessarily that the material is intrinsically safe,” he said.

That real world remains complicated. Mining, grinding, and shipping enough olivine could create emissions of its own. Scientists still need better ways to measure exactly how much carbon the ocean absorbs. And communities may resist plans to spread green mineral sand along their shores.

Hourglass Climate is now monitoring a larger Vesta trial off Duck, North Carolina, where they placed 8,200 tons of olivine offshore in 2024. Early results suggest abundance and diversity recovered there too, though metal analyses are still underway.