Note: Dead zones are areas of water so devoid of oxygen that sea life cannot live there. If phytoplankton productivity is enhanced by fertilizers or other nutrients, more organic matter is produced at the surface of the ocean. The organic matter sinks to the bottom, where bacteria break it down and release carbon dioxide. Bacteria thrives off excessive organic matter and absorb oxygen, the same oxygen that fish, crabs and other sea creatures rely on for life. Animator: Susan Twardy (HTSI). Scientist: Gene Feldman (NASA/GSFC). Writer: Rani Chohan (NASA/GSFC).