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Marine Phytoplankton observed with global biooptical methods
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Marine phytoplankton contributes 30 to 60% to the global primary production, but only 1 to 2% to the global biomass. Therefore, the functioning of the entire ecosystem of the world’s ocean depends on the energy produced entirely through the photosynthetic activity of these phytoplankton confined to the thin layer of lighted ocean surface waters. By that they are playing a key role in the biological pump for carbon sequestration and determining whether a part of the ocean is a carbon sink or source. Different functional groups of phytoplankton are playing different roles in the global biogochemical fluxes: biomineralizer (e.g. silicate), calicifiers, DMSP producers (which enforces cloud formation), toxic algae (causing high fish mortality), notrogen fixers, … It is important to be able to observe these phytoplankton populations on long time and large spatial scales in order to understand the mechanisms, variability and change and to provide a basis for numerical models, which can be used to simulate the ecosystem development for use, e. g. in fisheries management.
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On the other hand, the ocean carbon cycle and associated carbon fluxes are partly controlled by marine phytoplankton as the high number of their primary production indicates. Phytoplankton cells use inorganic carbon to photosynthesize organic matter, which in turn is recycled in the water column or exported towards sediments. To identify the different phytoplankton functional groups globally and thus proper model their growth in the global ocean is thus a prerequisite to the modeling of the marine carbon cycle and ecosystem. Through a better knowledge of the sinks and sources of CO2 in the ocean a contribution is made to a better understanding of changes in the world's climate as well as to the understanding of the marine food web.
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