Biological pump - (n.)
On short time scales, when compensating geochemical adjustments (e.g. changes in weathering processes on land and deposition and dissolution of calcium carbonate-rich sediments) can be neglected, the ocean's “productivity” (see definition below) is an important control on the partial pressure of atmospheric CO2. The biological pump runs on photosynthesis, which can be visualized as the fixation of dissolved carbon into particles, and relies on the settling of such particles out of the sunlit zone into deeper waters. In this manner, the biological pump removes carbon from the interface between ocean and atmosphere. The atmosphere, as a result, has less carbon dioxide than it would have otherwise. The efficiency of the pump is controlled by the amount of nutrients available to drive the process. Thus, if somehow the nutrient content of the ocean were increased, the biologic pump would be more efficient, and the CO2 of the atmosphere would drop. An increase in nutrients in the ocean during glacial periods was proposed by Wallace Broecker to explain the lowered CO2 content of the atmosphere measured in the air recovered from polar ice. The effect is one of many that must be considered when attempting to explain the fluctuations in CO2 during the ice ages.