Carbon enters the ocean primarily through the absorption of carbon dioxide (CO2) from the atmosphere at the ocean surface. This process occurs where air meets water, and is enhanced by wind, waves, and turbulence that increase the contact between the atmosphere and seawater, allowing CO2 to dissolve into the water

. The amount of CO2 absorbed depends largely on the difference in partial pressure of CO2 between the atmosphere and the surface seawater. When the partial pressure of CO2 in the atmosphere is higher than in the water, CO2 dissolves into the ocean until equilibrium is reached

. Cold water, especially in polar regions, absorbs more CO2 because gas solubility increases with lower temperatures. This cold, carbon-rich water becomes denser and sinks, transporting dissolved carbon into the deep ocean through a process called the physical carbon pump

. In addition to this physical process, biological activity also plays a key role. Phytoplankton in the ocean absorb CO2 during photosynthesis, converting it into organic carbon that supports marine life. When these organisms die, some of the carbon sinks to deeper waters or the seafloor, effectively sequestering carbon for longer periods

. Chemically, dissolved CO2 reacts with seawater to form carbonic acid, which dissociates into bicarbonate and carbonate ions. These forms of inorganic carbon are more stable and remain in the ocean, contributing to the ocean's large carbon reservoir

. In summary, carbon gets into the ocean through:

• Direct dissolution of atmospheric CO2 at the ocean surface, influenced by temperature, salinity, and wind

• Physical transport of carbon-rich cold water sinking to the deep ocean (physical carbon pump)

• Biological uptake by phytoplankton and subsequent sinking of organic carbon (biological carbon pump)

• Chemical conversion of CO2 into bicarbonate and carbonate ions that remain dissolved in seawater

These combined processes make the ocean the largest active carbon reservoir on Earth, holding about 95% of the surface carbon pool and playing a critical role in regulating atmospheric CO2 and global climate