Six potential CDR methods are recognized by the US National Academy of Sciences in a 2021 report:
Nutrient Fertilization — adding nutrients such as phosphorus or nitrogen to the ocean surface to increase photosynthesis.
Artificial Upwelling and Downwelling — Upwelling moves cooler, more nutrient- and CO2-rich deep water to the surface, stimulating the growth of phytoplankton, which absorb atmospheric carbon dioxide. Downwelling moves surface water and carbon to the deep ocean.
Seaweed Cultivation — Large-scale seaweed farming that transports biomass carbon to the deep ocean or into sediments.
Ecosystem Recovery — Carbon removal and sequestration through protection and restoration of coastal ecosystems and the recovery of fish, whales, and other marine wildlife
Ocean Alkalinity Enhancement — chemically altering ocean water to increase its alkalinity in order to enhance reactions that take up atmospheric CO2.
Electrochemical Processes— passing an electric current through water, these processes can either increase the acidity of seawater in order to release CO2, or increase the alkalinity of seawater to enhance its ability to retain CO2.