Final answer:
The size of the ocean's phytoplankton population is directly related to the amount of carbon dioxide in the atmosphere.
Step-by-step explanation:
The size of the ocean's phytoplankton population is directly related to the amount of carbon dioxide in the atmosphere. Phytoplankton, which are microscopic algae, rely on carbon dioxide for photosynthesis, their primary source of energy. When there is a higher concentration of carbon dioxide in the atmosphere, more carbon dioxide is dissolved into the ocean, providing phytoplankton with the necessary resources to grow and multiply. As a result, the phytoplankton population increases in size.
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