Carbon Moving In The Biosphere (the living things) of the ocean
Rainwater from the atmosphere has carbon that has dissolved in it, and the acid will react with minerals on the rocks, and this causes them to gradually dissolve. The carbon atom is now in the Geosphere and is happily starting its journey!
Since rainwater breaks down rocks, it makes ions that eventually reach the ocean through streams and rivers. Now carbon is in the hydrosphere!!
Since marine plants perform photosynthesis just like regular plants, they take the carbon dioxide being carried in the water to successfully make glucose to build its own plant tissue, and there is also carbon in glucose. So, the carbon is still there!