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Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 years. [42] Phytoplankton need nitrogen in biologically available forms for the initial synthesis of organic matter. Ammonia and urea are released into the water by excretion from plankton.
Nitrogen enters the ocean through precipitation, runoff, or as N 2 from the atmosphere. Nitrogen cannot be utilized by phytoplankton as N 2 so it must undergo nitrogen fixation which is performed predominantly by cyanobacteria. [82] Without supplies of fixed nitrogen entering the marine cycle, the fixed nitrogen would be used up in about 2000 ...
The marine nitrogen cycle consists of complex microbial transformations which include the fixation of nitrogen, its assimilation, nitrification, anammox and denitrification. [78] Some of these processes take place in deep water so that where there is an upwelling of cold waters, and also near estuaries where land-sourced nutrients are present ...
In addition to carbon, organic matter found in phytoplankton is composed of nitrogen, phosphorus and various trace metals. The ratio of carbon to nitrogen and phosphorus varies from place to place, [14] but has an average ratio near 106C:16N:1P, known as the Redfield ratio. Trace metals such as magnesium, cadmium, iron, calcium, barium and ...
However, the composition of individual species of phytoplankton grown under nitrogen or phosphorus limitation shows that this N:P ratio can vary anywhere from 6:1 to 60:1. While understanding this problem, Redfield never attempted to explain it with the exception of noting that the N:P ratio of inorganic nutrients in the ocean interior was an ...
Benthic-pelagic coupling are processes that connect the benthic zone and the pelagic zone through the exchange of energy, mass, or nutrients. These processes play a prominent role in both freshwater and marine ecosystems and are influenced by a number of chemical, biological, and physical forces that are crucial to functions from nutrient cycling to energy transfer in food webs.
In general, nitrogen tends to be a limiting ocean nutrient, but in HNLC regions it is never significantly depleted. [1] [2] Instead, these regions tend to be limited by low concentrations of metabolizable iron. [1] Iron is a critical phytoplankton micronutrient necessary for enzyme catalysis and electron transport. [3] [4]
Diagram of new and regenerated production with nitrification confined to the aphotic zone. This was used to frame the f-ratio and its link to export production. Bio-available nitrogen occurs in the ocean in several forms, including simple ionic forms such as nitrate (NO 3 −), nitrite (NO 2 −) and ammonium (NH 4 +), and more complex organic forms such as urea ((NH 2) 2 CO).