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Hmm, I'm not sure I would describe it like that - but sort-of.
Basically the carbon in the ocean (ie. from dead organisms) settles on the ocean floor, given lots of time and pressure it forms oil. Which is then used as a fossil fuel. However the carbons' main route from the atmosphere into the ocean - in terms of fossil fuels - is via photosynthesis where carbon is fixed from the atmosphere into aquatic plant life which is then eaten.
I gave a pretty bad definition of how oil is formed so I suggest you have a read of this to get a better idea of it :P
(gosh, I had no idea how hard it would be to find an internet resource on this subject.. how unexpected! - i'll see if I can find you a more solid source)
You also can't forget how carbon, in a gaseous form, becomes dissolved in water: http://harvardmagazine.com/2002/11/the-ocean-carbon-cycle.html
It is probably a good idea for you to look up carbon cycling/ the carbon cycle :)