A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period.The process by which carbon sinks remove carbon dioxide (CO 2) from the atmosphere is known as carbon sequestration.Public awareness of the significance of CO 2 sinks has grown since passage of the Kyoto Protocol, which promotes their use as a form of carbon offset.orests are carbon stores, and they are carbon dioxide sinks when they are increasing in density or area. In Canada's boreal forests as much as 80% of the total carbon is stored in the soils as dead organic matter.