The chemistry copies a natural process. When rain falls, it absorbs CO₂ from the air and becomes slightly acidic. If the rain then contacts an alkaline rock such as limestone, a small amount of the rock dissolves, neutralising the acid and turning the CO₂ into bicarbonate.

In pHathom’s reactor, seawater is first made acidic by passing it through the exhaust of a biomass power plant. The acidic water is then mixed with fine limestone particles. The reaction converts the captured CO₂ into bicarbonate, and the resulting solution is discharged back to the sea at the same pH as normal seawater.

The ocean has already taken up roughly 30 percent of all human‑caused carbon emissions since the 1980s. By adding more bicarbonate, the method aims to store additional carbon in the ocean for tens of thousands of years, extending the ocean’s natural role as a carbon sink.

Co‑founder and CEO Kimberly Gilbert said the pilot is the first step in showing the approach is safe and effective. “Climate change is a global problem, but putting something in somebody's local ocean is a local problem … so the local solution has to be demonstrated and proven as safe,” she explained.