Blue carbon is a concept within climate change mitigation that refers to "biologically driven carbon fluxes and storage in marine systems that are amenable to management." Most commonly, it refers to the role that tidal marshes, mangroves and seagrasses can play in carbon sequestration. These ecosystems can play an important role for climate change mitigation and ecosystem-based adaptation. However, when blue carbon ecosystems are degraded or lost they release carbon back to the atmosphere, thereby adding to greenhouse gas emissions.
The methods for blue carbon management fall into the category of "ocean-based biological carbon dioxide removal (CDR) methods". They are a type of biological carbon fixation.
Scientists are looking for ways to further develop the blue carbon potential of ecosystems. However, the long-term effectiveness of blue carbon as a carbon dioxide removal solution is under debate. 
The term deep blue carbon is also in use and refers to storing carbon in the deep ocean waters.