The first ship-based ocean alkalinity enhancement (OAE) experiment just delivered results. Woods Hole Oceanographic Institution poured 65,000 litres of sodium hydroxide into the Gulf of Maine in August 2025, and the findings are cautiously encouraging: 2–10 tonnes of CO₂ removed in four days, with up to 50 tonnes estimated total. No significant impact on marine life detected.
Adam Subhas and his team presented these findings at the Ocean Sciences Meeting 2026 in Glasgow. “We can definitely say that there was additional CO₂ uptake as a result of this experiment,” Subhas said.
The Honest Caveats
This isn’t a blank check for ocean CDR. Subhas acknowledged a critical gap: they haven’t yet estimated the emissions required to manufacture the sodium hydroxide and transport it to the site. Without that lifecycle analysis, net removal is unconfirmed.
That honesty matters. Several companies are already selling carbon credits based on alkalinity enhancement. Having non-commercial, independent trials that publish openly — including the uncomfortable questions — is exactly what the field needs.
What OAE Actually Does
The oceans have absorbed over a quarter of humanity’s excess CO₂, which is acidifying seawater and threatening marine organisms. OAE works by adding alkaline substances to counteract this acidification, which simultaneously increases the ocean’s capacity to absorb more CO₂ from the atmosphere.
Think of it as restoring the ocean’s natural carbon sink capacity rather than engineering something entirely new.
Researchers are testing multiple approaches: adding magnesium hydroxide to wastewater outflows, spreading ground olivine on coastlines, and pumping seawater through land-based treatment plants. Each has different cost profiles, scalability constraints, and ecological questions.
CDI’s View
Ocean CDR is one of the pathways we watch closely. The scale potential is enormous — oceans cover 71% of Earth’s surface and already store vastly more carbon than the atmosphere. But scale potential and proven, measurable removal are different things. This trial is a step toward the evidence base ocean CDR needs. Many more are needed.
Sources: New Scientist, Chemistry World