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How does carbon enter the ocean from the atmosphere?

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A labeled diagram of the periodic table entry for carbon, showing its atomic number 6, symbol C, electron configuration, atomic weight range, solid physical state, hexagonal crystal structure, and weakly acidic oxide properties. Color coding and icons indicate it is a nonmetal, solid at room temperature, with hexagonal structure and weak acidity. — carbon Carbon and its properties.

Carbon enters the ocean from the atmosphere primarily through the dissolution of carbon dioxide (CO₂) into the ocean's upper layers. This physical process occurs as the gas moves from the air into the surface waters.1

Additionally, carbon is incorporated into the ocean through biological processes:

Photosynthesis: Marine phytoplankton and other algae at or near the ocean surface take in atmospheric CO₂ and convert it into organic carbon through photosynthesis.12
Food Web Transfer: Once carbon is fixed by these organisms, it is passed through the marine food chain to other organisms, such as zooplankton.1

While these processes facilitate the movement of carbon into the ocean, human activities—specifically industrial and agricultural processes—have significantly increased the amount of atmospheric CO₂ absorbed by the oceans since the Industrial Revolution, leading to ocean acidification.31