Ocean alkalinity enhancement (OAE) is a proposed marine carbon dioxide removal (mCDR) approach that accelerates the ocean's natural chemical weathering process. By adding alkaline materials—such as crushed olivine, limestone, lime (calcium hydroxide), or electrochemically generated sodium hydroxide—to surface seawater, OAE raises the water's pH and shifts the carbonate equilibrium, converting dissolved CO2 into bicarbonate and carbonate ions. This increases the ocean's capacity to draw down additional atmospheric CO2 and, in principle, stores the resulting carbon for tens of thousands of years.
OAE is part of a broader family of mCDR techniques discussed in IPCC assessment reports, including the Sixth Assessment Report (AR6, 2021–2022), which catalogued ocean-based removal options alongside afforestation, direct air capture, and bioenergy with carbon capture and storage. The technique is still largely at the research and small-pilot stage.
Key governance and policy issues include:
- Marine pollution law. Additions of substances to the ocean intersect with the London Convention (1972) and the London Protocol (1996), whose 2013 amendment created a framework for regulating marine geoengineering activities, initially focused on ocean fertilization.
- UNCLOS obligations. Parties to the UN Convention on the Law of the Sea must prevent marine pollution and assess transboundary environmental impacts (Articles 192, 194, 206).
- Convention on Biological Diversity. CBD decisions (notably COP-10 decision X/33 in 2010) call for caution on climate-related geoengineering pending adequate scientific basis and risk assessment.
- Monitoring, reporting, and verification (MRV). Quantifying actual CO2 uptake attributable to alkalinity additions is technically difficult and central to any carbon-crediting regime.
Environmental concerns include local pH spikes, heavy-metal content of some mineral feedstocks (e.g., nickel and chromium in olivine), effects on marine ecosystems, and the energy and emissions cost of mining, grinding, and transporting alkaline materials at climate-relevant scales.
Example
In 2023, the U.S. start-up Planetary Technologies began a small field trial off Halifax, Nova Scotia, releasing magnesium hydroxide into a wastewater outfall to test alkalinity enhancement under a Canadian regulatory permit.
Frequently asked questions
There is no OAE-specific treaty. It is subject to general obligations under UNCLOS, the London Convention/Protocol, and the CBD. The London Protocol's 2013 marine geoengineering amendment could extend to OAE if parties list it, but that amendment has not yet entered into force.
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