Ocean alkalinity enhancement (OAE) is a geo-engineering technique and carbon dioxide removal (CDR) technology that involves adding alkaline substances, such as crushed limestone (carbonate rock) or calcium hydroxide and olivine (silicate rock), to the ocean in order to increase its alkalinity. This technology has the theoretical potential to sequester 1–15+ Gt CO2/ year with a residence time of ~10,000 years¹.
There are several ways to add alkalinity to the ocean. These include spreading finely ground alkaline substances over the open ocean, depositing alkaline sand or gravel on beaches or coastal seabeds, and reacting seawater with alkaline minerals inside specialised fuel cells before releasing it back into the ocean. These can be seen in figure 1.
The Ocean, Climate Change and Increase of Atmospheric CO2 Concentration
Oceans cover ⅔’s of the world’s surface, absorbing 90% of the Earth’s excess heat and removing approximately ¼ of CO2 from the atmosphere.²
In the 200 years since the industrial revolution began, the concentration of CO2 in the atmosphere has increased due to anthropogenic activity and subsequently caused the ocean’s sea level, temperature and acidity to increase. These dramatic changes in the ocean’s properties are impacting the biosphere: harming marine life, supply chains, and human livelihoods.
The process of OAE aims to reduce the amount of carbon dioxide in the atmosphere by increasing the ocean’s capacity to absorb it. When CO2 dissolves in seawater, where the rate of CO2 entering the ocean has increased due to anthropogenic activity, it reacts with water to form carbonic acid, which lowers the pH of the ocean and makes it more acidic.
OAE can help counteract the process of ocean acidification and reduce the overall impact of carbon dioxide emissions on the environment.
Why Ocean Acidification is Such a Problem
OAE is considered one of the most promising CDR technologies with its potential impact due to the size of the ocean and ability to reverse ocean acidification, while also decreasing the CO2 in the atmosphere. Surface ocean waters have fallen by 0.1 pH units from 8.1 which unintuitively, due to the pH scale being logarithmic, represents a drastic 30% increase in ocean acidity.³
If the ocean tips past certain acidic thresholds, it is considered to unlock a positive feedback loop that will accelerate climate change and change ecosystems at an alarming rate until a new equilibrium is established, that will cause the extinction of many species of aquatic life and severely dampen human livelihoods. A diagram representing thresholds and system science of this can be seen in figure 2. Considering the size of the ocean as a carbon sink and the interconnectedness of it to all functions of the biosphere and human livelihoods this is a serious consequence that needs to be avoided.