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Phytoplankton obtain energy through the process of photosynthesis and must therefore live in the well-lit surface layer (termed the euphotic zone) of an ocean, sea, lake, or other body of water. Phytoplankton account for about half of all photosynthetic activity on Earth.
The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological processes that supply nutrients into the upper water column.
The marine carbon cycle. Carbon dioxide is taken up by phytoplankton for photosynthesis and incorporated into the marine food web. When plankton or predator dies, sedimentation of organic matter reaches the seafloor, where carbon can be buried and sequestered.
Schematic of photosynthesis in plants. The carbohydrates produced are stored in or used by the plant. Composite image showing the global distribution of photosynthesis, including both oceanic phytoplankton and terrestrial vegetation. Dark red and blue-green indicate regions of high photosynthetic activity in the ocean and on land, respectively.
Photosynthetic picoplankton or picophytoplankton is the fraction of the photosynthetic phytoplankton of cell sizes between 0.2 and 2 μm (i.e. picoplankton). It is especially important in the central oligotrophic regions of the world oceans that have very low concentration of nutrients.
Phytoplankton (from Greek phyton, or plant) are autotrophic prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis. Among the more important groups are the diatoms , cyanobacteria , dinoflagellates , and coccolithophores .
Like plants on land, phytoplankton use chlorophyll and other light-harvesting pigments to carry out photosynthesis, absorbing atmospheric carbon dioxide to produce sugars for fuel. Chlorophyll in the water changes the way the water reflects and absorbs sunlight, allowing scientists to map the amount and location of phytoplankton.
Photosynthesis by phytoplankton lowers the partial pressure of CO 2 in the upper ocean, thereby facilitating the absorption of CO 2 from the atmosphere by generating a steeper CO 2 gradient. [55] It also results in the formation of particulate organic carbon (POC) in the euphotic layer of the epipelagic zone (0–200 m depth).