To tackle the climate challenge, there is a pressing need for the deployment of carbon dioxide removal (CDR) technologies. One ocean-based CDR technique is ocean alkalinity enhancement (OAE), which proposes to increase the alkalinity content of seawater to stimulate the CO2 uptake of the surface ocean. A particular prominent implementation of OAE involves the addition of minerals to coastal and shelf sediments, which release alkalinity upon transformation in the seabed - termed “enhanced weathering”. Preliminary model estimates of the CDR potential of enhanced weathering are in the order of several gigatonnes CO2 per year.
Here, I will illustrate the potential of New Zealand for mineral-based OAE and evaluate alternative resources for mineral-based OAE, including silicates (basalt, kimberlite), carbonates and iron-based minerals. I will address the limitations of widespread mineral additions in the coastal zone, and argue that widespread deployment of mineral-based OAE is unlikely to achieve gigaton-scale CO2 drawdown, but a well-considered combination of different OAE technologies could buffer ocean acidification and increase oceanic CO2 uptake on local and regional scales. Optimal deployment of mineral-based OAE technologies will require a good understanding of natural alkalinity generation in the seafloor and sediment transport in the coastal zone.