The biological pump is the process by which CO₂ fixed by photosynthesis is transferred to the deep ocean as dead organisms, skeletal and faecal material (Particulate organic carbon, POC and Particulate Inorganic carbon, PIC) resulting in sequestration (storage) of carbon for periods of decades to centuries (depending on the depth of remineralisation) or even permanently in the sediments. Permanent sequestration may be in the form of organic matter, the type of material that is the source of oil and natural gas, or calcium carbonate. The latter, mainly derived from planktonic sources such as the plates of coccolithophores and shells of foraminifera and the benthic corals of shallow warm seas has formed chalk, limestone and marble. In order to predict future CO₂ concentrations in the atmosphere, it is necessary to understand the way that the biological pump varies both geographically and temporally and the effects on the pump of changes in temperature, ocean circulation and ocean chemistry (e.g. acidification due to increased CO₂).