Editing The Global Carbon Cycle (section)

=== 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.