English: Components of the biological pump
The biological pump is responsible for transforming Dissolved Inorganic Carbon (DIC) into organic biomass and pumping it in particulate or dissolved form into the deep ocean. Inorganic nutrients and Carbon Dioxide (C02) are fixed during photosynthesis by phytoplankton, which both release Dissolved Organic Matter (DOM) and are consumed by herbivorous zooplankton. Larger zooplankton-such as copepods, egest fecal pellets - which can be reingested, and sink or collect with other organic detritus into larger, more-rapidly-sinking aggregates. DOM is partially consumed by bacteria (black dots) and respired; the remaining refractory DOM is advected and mixed into the deep sea. DOM and aggregates exported into the deep water are consumed and respired, thus returning organic carbon into the enormous deep ocean reservoir of DIC. About 1% of the particles leaving the surface ocean reach the seabed and are consumed, respired, or buried in the sediments. There, carbon is stored for millions of years. The net effect of these processes is to remove carbon in organic form from the surface and return it to DIC at greater depths, maintaining the surface-to-deep ocean gradient of DIC (inset graph at lower right). Thermohaline circulation returns deep-ocean DIC to the atmosphere on millennial timescales.