Carbon sink

A carbon sink is a natural or artificial reservoir that stores carbon-containing chemical compounds for a long period. Carbon sinks absorb more carbon than they release. 
A forest, ocean, or other natural environments produce surplus carbon. Carbon sinks are very important in our environment. They can be natural or man-made. Soil, ocean, forest and the atmosphere all store carbon and this carbon moves in a continuous cycle. The largest carbon sinks become swamps, bogs, and eventually coal measures.
In the regular carbon cycle, CO2 comes from the atmosphere and then is taken by plants and uses it in the process of photosynthesis.