Figure 12. The oceanic ‘biological carbon pump’ is a collective expression for planktonic, biological processes and feedback pathways that play a role in carbon transfer from the photic zone (zone of light penetration) to the the deep ocean. This complex ecosystem begins with phytoplankton using sunlight and dissolved inorganic nutrients to photosynthetically convert atmospheric CO2 into biogenic matter, which forms the base of the marine food web. The autotrophic and heterotrophic organisms excrete particles and dissolved matter as they grow and die. The particles sink through the water column carrying carbon to the deep ocean. Thus, the biological pump is one of the pathways that regulate atmospheric CO2 concentrations, the other being the physical ‘solubility pump’. Generally, the food web is efficient and most of the produced particles and dissolved organic matter is recycled through the microbial loop to CO2 and released back to the atmosphere. (Courtesy of International JGOFS Project Office, Norway).