Ocean Carbon Dioxide Removal and Storage.

The ocean, Earth's largest carbon reservoir, exerts a central role over atmospheric CO2 through its capacity to store carbon primarily as bicarbonate ions. Direct observations indicate that the global ocean has a net carbon uptake of 2.6-3.0 petagrams of carbon annually, representing nearly 30% of anthropogenic CO2 emissions. This review examines two principal domains of oceanic carbon cycling. The first concerns the natural uptake and storage of anthropogenic CO2, with emphasis on the response of the marine carbonate system and the spatial distribution of absorbed carbon. The second addresses emerging marine CO2 removal strategies, especially ocean alkalinity enhancement and macroalgae-based approaches. Ocean alkalinity enhancement aims to increase seawater buffering capacity to facilitate greater CO2 uptake, whereas macroalgae-based strategies rely on photosynthetic fixation and the subsequent storage of organic and inorganic carbon in various reservoirs. Effective implementation of these approaches necessitates rigorous monitoring, reporting, and verification frameworks to ensure their quantifiable efficacy and environmental integrity.