In August, a piece of the Atlantic suddenly turns dark red. For four days, a reddish stripe runs through the water in the Gulf of Maine off the US east coast. Research ships cross the zone. Autonomous submarines glide through the water column. Sensors measure every chemical change.

The reason for the unusual spectacle: Scientists pumped 65,000 liters of an alkaline solution of sodium hydroxide into the sea – consciously, in a controlled manner and marked with red dye.

The experiment was intended to temporarily reduce the acidification of seawater and at the same time capture more CO2 from the atmosphere. The previous laboratory tests were successful in theory. Now the researchers wanted to find out whether so-called ocean alkalinization can even be technically implemented in the open sea – and whether it remains harmless to the ecosystem.

Just pour chemicals into the sea for the climate?

Behind the experiment is an international team and the LOC‑NESS (“Locking away Ocean Carbon in the Northeast Shelf and Slope”) project led by the Woods Hole Oceanographic Institution. The head, oceanographer Adam Subhas, presented the results at the end of February at the “Ocean Sciences Meeting 2026″ (OSM 26) in Glasgow – one of the world’s largest marine science congresses.

The effects of the experiment are still manageable so far: extrapolated over a year, the experiment could bind around 50 tons of additional CO2 – about as much as five people emit annually. This is tiny for the global climate impact; Here, CO2 removals on a gigatonne scale would be necessary. But there is also positive news: Initial measurements showed no immediate damage to plankton or fish.

A remedy for ocean heartburn

The method works like an ocean heartburn remedy: The solution increases the alkalinity of seawater, allowing it to absorb and chemically bind more CO2 from the atmosphere.

An ecosystem under triple pressure

A measure that can save the seas locally, which is becoming increasingly important. Because the oceans – the largest ecosystem on earth – are under enormous stress. Heat waves are driving water temperatures in many regions to record highs, coral reefs are dying and fish stocks are coming under pressure. At the same time, nutrient inputs from agriculture and industry cause a lack of oxygen, especially in shallow coastal regions such as the Baltic Sea. So-called death zones in which life is hardly possible are becoming more and more common there.

Added to this is the acidification of the oceans. The oceans absorb large amounts of CO2 from the atmosphere – an important climate buffer. But the dissolved CO2 lowers the pH value of the water.

A report from the Potsdam Institute for Climate Impact Research warns that acidification is approaching critical thresholds. Lime-forming organisms such as mussels, corals and certain types of plankton are particularly at risk – their damage could destabilize entire food chains.

• To explain: CDR stands for Carbon Dioxide Removal – technologies that actively remove carbon dioxide from the atmosphere.

At the same time, Riebesell warns against excessive expectations. Ecological consequences must be carefully examined. It is also unclear whether ocean acidification can be combated permanently through local alkanization.

“Locally and temporarily, increasing alkalinity can counteract ocean acidification,” says Riebesell. As soon as the seawater is back in equilibrium with the atmosphere, the difference is small. The CO2 concentration in the air remains crucial.