Research trends in ocean alkalinity enhancement as an ocean-based negative emission technology

Abstract

This review summarizes recent advances in “ocean alkalinity enhancement (OAE)” technologies, in which carbonates and alkaline substances are introduced into the ocean to neutralize the acidified seawater and enhance carbon uptake by the ocean. Among “ocean-based negative emission technologies,” although the promotion of ocean carbon uptake through the blue carbon concept in coastal ecosystems has gained widespread societal recognition, and large-scale demonstration tests are currently being planned, OAE remains relatively underrecognized in Japan. However, OAE is increasingly regarded globally as a promising ocean-based CO₂ removal technology, and it is important to clarify its fundamental characteristics. The blue carbon concept focuses on the absorption and sequestration of atmospheric and oceanic CO₂ in the form of organic matter, whereas OAE aims to absorb atmospheric and oceanic CO₂ in the form of bicarbonate ions (HCO₃⁻) in seawater. It is essential to establish a small-scale experimental system in a laboratory or marine research station to clarify each process and identify optimal settings, evaluate CO₂ absorption effects, assess potential environmental impacts for field implementation, and conduct a comprehensive study from the perspective of social acceptability in preparation for future field-scale demonstration tests in the sea area.