Answer:
Phytoplanktons are microscopic creatures that are primary producers of oceans. Phytoplanktons take carbon dioxide from atmosphere to make their food and then they are eaten by some other animals of oceans.
Phytoplanktons are present in huge numbers in oceans and have a great contribution to the carbon cycle because it is responsible for the transfer of carbon dioxide from the atmosphere to the oceans.
Most of the carbon is released through combustion by animals that eat phytoplanktons but some accumulate in the ocean floor because some dead phytoplanktons settles down in the ocean.