How does the ocean solubility pump move carbon dioxide into deep water?

The ocean solubility pump is a physical process that facilitates the transport of atmospheric carbon dioxide (CO₂) into the deep ocean. This mechanism is driven by the solubility of CO₂ in seawater and the large-scale movement of ocean water masses.12

The process functions through the following steps:

• Surface Absorption: Atmospheric CO₂ dissolves into the surface layers of the ocean, where it reacts with water to form carbonic acid, which then dissociates into bicarbonate and carbonate ions.12
• Cooling and Density: In high-latitude regions, surface waters are cooled by the atmosphere. As water cools, its density increases, causing it to sink toward the ocean floor.12
• Deep-Water Transport: This sinking, cold, dense water carries the dissolved inorganic carbon from the surface into the deep ocean as part of the thermohaline circulation.2

Once this carbon reaches the deep ocean, it is effectively sequestered away from the atmosphere for long periods, as these deep waters are separated from the surface layers. This physical pump is a critical component of the global carbon cycle, helping to regulate the concentration of CO₂ in the atmosphere.234