Blue carbon refers to carbon absorbed and stored by marine ecosystems such as seaweed, and was defined in the 'Blue Carbon' report published by the United Nations Environment Programme (UNEP) in 2009. It was introduced as a new option for carbon sequestration strategies, similar to 'green carbon,' which is carbon absorbed and stored by terrestrial ecosystems.

The main sinks for blue carbon are algal beds (seaweed and seagrass), salt marshes such as tidal flats, and mangrove forests, which are called ‘blue carbon ecosystems’.

The mechanism of absorption involves carbon dioxide (CO2) being released into the atmosphere, dissolving into the ocean, and being absorbed by marine organisms through photosynthesis. When these organisms die, they settle on the seafloor, where the carbon is stored.

A major reason for the recent interest in blue carbon is the amount of carbon dioxide absorbed and its sequestration period. While the entire land absorbs 1.9 billion tons of carbon, the entire ocean absorbs 2.9 billion tons, about 1.5 times the amount of carbon absorbed on land*. As for the sequestration period, blue carbon sequestrates carbon for hundreds to thousands of years, while green carbon is said to sequester for only a few decades.

*Excerpt from the Ministry of Land, Infrastructure, Transport and Tourism, Port Bureau:
'Marine Forests and Blue Carbon'

Areas where seaweeds thrive are called 'seaweed beds.' Also known as 'cradles of the sea,' these areas play an important role in the marine ecosystem as sites for environmental conservation, and as spawning and hiding grounds for fish and other aquatic organisms. However, environmental changes caused by rising seawater temperatures and feeding damage by algae-eating animals (e.g., sea urchins) have led to a significant decrease or disappearance of seaweed, resulting in a phenomenon known as 'barren reefs' occurring worldwide.
Therefore, it is extremely important to focus on the conservation and creation of seaweed beds, including aquaculture efforts.

Seaweeds have been considered beneficial to health since ancient times, with various effects and benefits reported from their dietary fibers and polysaccharides. In addition to being eaten as a food, its components, such as alginic acid, carrageenan, and cantenes, are used in a very wide range of fields, including medical and industrial applications. By deepening our understanding of seaweeds and incorporating them into our diet, we can help increase seaweed cultivation. As a result, seaweed farming will increase, which will lead to the preservation and creation of seaweed beds, contributing to the creation of 'blue carbon.'