Blue carbon

Blue carbon is the carbon captured by the world's oceans and coastal ecosystems. The carbon captured by living organisms in oceans is stored in the form of biomass and sediments from mangroves, salt marshes and seagrasses.

Relevance of blue carbon
The rates of blue carbon sequestration and storage capacities in ecosystems are comparable to (and often higher than) those in carbon-rich terrestrial ecosystems such as tropical rainforests or peatlands. Unlike most terrestrial systems, which reach soil carbon equilibrium within decades, deposition of carbon dioxide in coastal ecosystem sediment can continue over millennia. However, when these coastal ecosystems are degraded or destroyed they can become carbon dioxide sources due to the oxidization of biomass and organic soil.

Because coastal ecosystems do contain substantial amounts of carbon, and because this carbon is in danger of being released, they are important in mitigating climate change. However, the rate of loss of mangroves, sea grasses and salt marshes (driven mostly by human activities) is estimated to be among the highest of any ecosystem on the planet, prompting international interest in managing them more effectively for their carbon benefits.

These ecosystems are highly valuable not only for their contribution to climate change mitigation on a global scale, but also for the many valuable services they provide locally.

Various processes are known to enhance the ocean's ability to store carbon. Sperm whales increase the levels of primary production and carbon export to the deep ocean by depositing iron rich faeces into surface waters of the Southern Ocean. The iron rich faeces causes phytoplankton to grow and take up more carbon from the atmosphere. When the phytoplankton dies, it sinks to the deep ocean and takes the atmospheric carbon with it. By reducing the abundance of sperm whales in the Southern Ocean, whaling has resulted in an extra 2 million tonnes of remaining in the atmosphere each year.