Fjords are massive carbon sinks that trap huge amounts of carbon in their deep sediments.

Fjords are deep, narrow glacial valleys flooded by seawater that act as highly efficient natural carbon traps. A 2015 study published in the journal Nature Geoscience by researchers from the University of Bergen and the University of Florida highlighted their disproportionate role. Although they occupy only 395,000 square kilometers of the ocean floor, they sequester approximately 18 million metric tons of organic carbon every year.The unique geomorphology of fjords contributes to this efficiency. They often feature a shallow sill at the mouth that restricts water circulation, leading to stagnant, oxygen-depleted bottom waters. This anoxic environment slows down the bacterial breakdown of organic material, such as dead plankton and terrestrial debris. As a result, the carbon remains buried in the seabed rather than being released back into the atmosphere as carbon dioxide.Research indicates that fjord sediments bury carbon at a rate of 210 grams per square meter annually. This rate is significantly higher than the global ocean average of about 5 grams per square meter. Because they are located near steep mountains, fjords also receive a high volume of terrestrial organic matter from runoff, which adds to the carbon pool. These geological features serve as critical long-term storage sites that help mitigate the effects of global warming.