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 CO_2 in the air to produce organic carbon and release O_2 through photosynthesis. Besides supporting the ocean ecosystem, photosynthetically produced 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 CO_2 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.