This allows the oceans to absorb additional carbon dioxide from the atmosphere. If fewer phytoplankton existed, atmospheric carbon dioxide would increase. Click here for a diagram of the Carbon Cycle. Phytoplankton also affect carbon dioxide levels when they die. Phytoplankton, like plants on land, are composed of substances that contain carbon.
Dead phytoplankton can sink to the ocean floor.
The carbon in the phytoplankton is soon covered by other material sinking to the ocean bottom. In this way, the oceans act as a sink, a place to dispose of global carbon, which otherwise would accumulate in the atmosphere as carbon dioxide. Other global sinks include land vegetation and soil. However the carbon in these sinks frequently is returned to the atmosphere as carbon dioxide by burning or decomposition. Deforestation contributes to the accumulation of carbon dioxide in the atmosphere by reducing vegetation that takes up carbon dioxide.