Oceans | VOL. 11, ISSUE 67, July-August 2011

Nitrogen and the North East Arabian Sea

Most plants and bacteria produce energy that the rest of the ecosystem can use, and are the primary producers; and, the rate at which they produce the energy is labelled productivity which plays a crucial role in the global carbon cycle. Roughly half of this productivity occurs in the oceans, by microscopic plants called plankton. Thus, ocean primary productivity (OPP) is defined as the carbon per unit time and unit area set by the ocean phytoplankton’s photosynthesis. New productivity is part of the oceanic primary productivity supported by nitrates, brought into the euphotic (sunlit) zone from deeper waters through a physical processes; while regenerated productivity is productivity supported by ammonium and urea, derived from biological processes occurring within the euphotic zone. Regenerated production is fuelled by nitrogen recycled biologically in the euphotic zone, ammonium (NH) being the principal form. New production, on the other hand, is fuelled by external sources, primarily in the form of nitrate (NO3) supplied principally by vertical mixing from below the euphotic zone (R C Dugdale and J J Goering (1967); Uptake of new and regenerated forms of nitrogen in primary productivity; Limnol. Oceanogr.). The availability of the nutrients is influenced by biological and physical processes like upwelling, mixing, advection and diffusion. In the sunlit zone, under a steady state - i.e. the absence of significant lateral transport, the loss of...

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