Description
Ocean Alkalinity Enhancement (OAE) is based on a simple idea: adding alkaline material to the ocean to increase the capacity of seawater to absorb CO₂ from the air and effectively store it in the form of bicarbonate. OAE is accelerating a process that is occurring naturally, through land weathering and carbonate dissolution in the seawater, but the potential impacts on marine life are poorly understood. One of the possible substances for implementing OAE is slaked lime (calcium hydroxide), which is made by processing limestone. The spreading of slaked lime by ships during regular maritime traffic has been proposed as a way to scale OAE.
Scientists from across Europe came together in this project to test ocean liming in a controlled, scientific way. The team focused on two very different marine environments:
- The ultra-nutrient-poor (oligotrophic) waters around Crete and Greece, and
- The nutrient-rich (eutrophic) waters near Vigo, Spain.
They used two main types of experiments:
- Microcosms – small-scale lab-based systems with 15–45 liters of seawater in each tank.
- Mesocosms – much larger enclosures holding over 1,000 liters of seawater in each tank, which better represent the marine environment.
Across both sites and systems, the researchers tested different amounts of slaked lime to observe the effects on:
- Seawater chemistry (pH and alkalinity),
- Plankton communities,
- Calcareous marine algae (benthic coralline algae and planktonic coccolithophorids),
- CO₂ absorption potential and stability.
In total, over 120 days of experiments were conducted with the help of more than 20 scientists and technicians.