Editing The Global Carbon Cycle (section)

== Oceanic Absorption ==

The global ocean is the largest active carbon reservoir on Earth, holding roughly 50 times more carbon than the atmosphere. The ocean continuously exchanges CO2 with the lower atmosphere through two primary mechanisms: the physical (solubility) pump and the biological pump.

=== The Physical Pump ===
Carbon dioxide is highly soluble in water. At the air-sea interface, CO2 dissolves directly into the ocean's surface waters, reacting with water molecules to form carbonic acid, bicarbonate, and carbonate ions. 

The physical pump is driven by ocean temperatures and global thermohaline circulation. Cold water can hold significantly more dissolved gas than warm water. Therefore, cold surface waters in the North Atlantic and Southern Ocean absorb massive amounts of CO2. Because these cold waters are highly dense, they sink to the deep ocean basin, effectively dragging the dissolved carbon away from the atmosphere and sequestering it in the deep ocean for centuries to millennia.

=== The Biological Pump ===
Marine ecosystems also actively draw down carbon. Microscopic phytoplankton living in the sunlit surface waters perform photosynthesis, incorporating dissolved CO2 into their cellular structures. When these organisms—and the predators that consume them—die, a portion of their organic matter sinks into the deep ocean. This continuous shower of organic detritus is known as '''marine snow'''. 

Additionally, many marine organisms (like corals, oysters, and certain plankton) extract dissolved carbon and calcium from the water to build calcium carbonate shells. When they die, these shells sink to the ocean floor, eventually compacting over geological time to form massive limestone deposits, transferring carbon from the fast cycle into the slow, geological cycle.