What is the principal mechanism by which the ocean acts as a carbon sink?

The principal mechanism by which the ocean acts as a carbon sink is the dissolution of atmospheric carbon dioxide (CO2) into seawater, followed by chemical reactions that convert the dissolved CO2 into other forms of carbon. A carbon sink is a natural or artificial reservoir that accumulates and stores carbon-containing chemical compounds for an indefinite period, thereby removing CO2 from the atmosphere. When atmospheric CO2 dissolves in seawater, it undergoes a series of chemical reactions. First, CO2 reacts with water (H2O) to form carbonic acid (H2CO3). Carbonic acid then dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+). Bicarbonate ions can further dissociate into carbonate ions (CO32-) and more hydrogen ions. These reactions are reversible, and the equilibrium between the different forms of dissolved inorganic carbon (CO2, H2CO3, HCO3-, CO32-) depends on factors such as temperature, salinity, and pH of the seawater. The formation of bicarbonate and carbonate ions effectively increases the ocean's capacity to absorb more CO2 from the atmosphere, as these ions act as buffers that neutralize the acidity caused by the dissolution of CO2. Furthermore, marine organisms, such as phytoplankton and shellfish, utilize dissolved CO2, bicarbonate, and carbonate ions to build their shells and skeletons through a process called biogenic calcification. When these organisms die, their remains sink to the ocean floor, where they can be buried in sediments, effectively storing carbon for long periods. This process is known as the biological pump. The combination of chemical dissolution and biological processes makes the ocean a significant carbon sink, absorbing a substantial portion of the CO2 emitted by human activities.