OAE: Ocean Alkalinity Enhancement

Among the ocean-based CDRs, Ocean Alkalinity Enhancement (OAE) is considered a particularly promising option for carbon dioxide (CO₂) removal. The basic idea is to accelerate a natural process, rock weathering. When rock minerals react with water and atmospheric CO₂, they bind the CO₂ as dissolved bicarbonate or carbonate. There is 35 times more bicarbonate or carbonate dissolved in the ocean than CO₂ gas in the atmosphere, so small changes in the ocean’s large pool of inorganic carbon can make a big difference for the atmospheric CO₂ concentration. A positive side effect of dissolving alkaline minerals in seawater is that it reverts ocean acidification, a direct consequence of rising levels of atmospheric CO₂.

Whether or not OAE could work at the scale needed to contribute significantly to CDR depends on three aspects: feasibility, cost and environmental compatibility. Research so far has focused mostly on feasibility and cost assessments which revealed a high competitiveness relative to other Negative Emission Technologies (NETs). However, any promising prospects with respect to feasibility become irrelevant if their application is accompanied by unacceptable environmental side effects.

Ocean-CDR sets out to test for possible environmental impacts and side effects of OAE. This is done in so-called mesocosms, large translucent plastic bags anchored in the sea, which enclose a natural plankton community - from algae and bacteria over little protozoans up to crustaceans and sometimes even fish. Thus, in the mesocosms, we can simulate OAE in a natural plankton community under natural conditions, but securely enclosed in the bags.