Bach (2024): The additionality problem of ocean alkalinity enhancement

Lennart Thomas Bach IN: Biogeosciences, 21, https://doi.org/10.5194/bg-21-261-2024

So far, feasibility studies on OAE have mainly focused on enhancing alkalinity in the oceans to stimulate CO₂ sequestration (C_OAE); however, the primary focus has not been on how such anthropogenic alkalinity would modify the natural alkalinity cycle and associated baseline CO₂ sequestration (ΔC_baseline). Here, the author present incubation experiments in which materials considered for OAE (sodium hydroxide, steel slag, and olivine) are exposed to beach sand to investigate the influence of anthropogenic alkalinity on natural alkalinity sources and sinks. The experiments show that anthropogenic alkalinity can strongly reduce the generation of natural alkalinity, thereby reducing additionality. This is because the anthropogenic alkalinity increases the calcium carbonate saturation state, which reduces the dissolution of calcium carbonate from sand, a natural alkalinity source. He argues that this “additionality problem” of OAE is potentially widespread and applies to many marine systems where OAE implementation is considered – far beyond the beach scenario investigated in this study.

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