Macroalgal photosynthesis is a major source of marine primary productivity and a crucial part of the ocean carbon cycle. Macroalgae effectively absorb inorganic carbon dissolved in the ocean and CO2 in the air to produce or- ganic carbon and release O2 through photosynthesis. Besides supporting the ocean ecosystem, photosynthetically pro- duced products are deposited in the sediment in the form of organics to complete the carbon sink. Proliferation of macroalgae results in a significant decrease in CO2 concentration, mitigates ocean acidification, strengthens the effect of ocean carbon sequestration, and mitigates climate change. These results provide a general description of the mechanism and potential of macroalgae to contribute to the carbon sink and present ways to enhance ocean carbon sink capacity. The results provide a basis for developing a macroalgal carbon sink effects study.