Phytoplankton biogeochemical cycles

Carbon, nitrogen and phosphorus are essential elements required for all life on Earth. In the marine environment, dissolved inorganic carbon, nitrogen and phosphorus are utilized during phytoplankton growth to form organic material, which is respired and remineralized back to inorganic forms by the activity of bacteria, Archaea and zooplankton. The net result of the photosynthesis, calcification and respiration of marine plankton is the uptake of carbon dioxide (CO2) from the atmosphere, its sequestration to the deep ocean as organic and inorganic carbon and its availability to fuel all fish and shellfish production. The cycling of carbon by marine plankton is inextricably linked to that of nitrogen and phosphorus; thus marine plankton mediate climate through influencing the atmospheric concentration of not only CO2, but also nitrous oxide (N2O). Increasing anthropogenically derived atmospheric CO2 concentrations impact plankton mediated biogeochemical cycles through increasing seawater temperature and dissolution of CO2, leading to changes in water column mixing, availability of light and nutrients, decreasing dissolved oxygen and changing carbonate chemistry. This chapter describes how the activity of phytoplankton, bacteria and Archaea drive the marine biogeochemical cycles of carbon, nitrogen and phosphorus, and how climate driven changes in plankton abundance and community composition are influencing these biogeochemical cycles in the North Atlantic Ocean and adjacent seas