Phytoplankton global distribution

B Sundstrom, L Edler, E Graneli. The global distribution of harmful effects of phytoplankton. In E Graneli, B Sundstrom, L Edler and DM Anderson, eds. Toxic Marine Phytoplankton. Amsterdam Elsevier, 1990, pp. 537-541. 

The presence and distribution of phytoplankton in the sea is determined primarily by the abundance of chlorophyll. Although this is not a direct measure of the number of cells, because they contain different amounts of chlorophyll under different conditions, it is the most rapid and widely used method of identifying the presence of photosynthetic organisms. Because the color of the ocean can be determined by satellites, it is possible to determine the global content of chlorophyll in the sea over one optical depth, about the first 30 m of surface waters. 

Turning to Table I it is obvious that by far the largest share (75% according to Woodwell et al. 1978) in the global marine net primary production comes from the open oceans and hence from the phytoplankton in that system. It is at the same time remarkable that this production is out of proportion in relation to the phytoplankton biomass 26% of the total aquatic marine plant mass could be estimated in the open ocean. It should be realised that the distribution of phytoplankton in the sea is rarely uniform and frequently extremely patchy. Horizontally, patches are usually elliptical and vary in size from a few metres to hundreds of kilometres across. Long narrow bands or streaks, a few metres in width, are common and may form a pattern superimposed on that of the patches. Under conditions of strong mixing, vertical distribution of phytoplankton may be uniform, but if the water column becomes stabilised, non-motile forms denser than water will... 

Microscopic plant life— phytoplankton—is scarce in certain parts of the ocean (Figure 1.22 T). Several years ago scientists proposed that this scarcity is caused by the lack of plant nutrients, primarily iron. Because phytoplankton take up carbon dioxide in photosynthesis, it was also proposed that relatively small amounts of iron distributed in appropriate regions of the oceans could reduce atmospheric carbon dioxide, thereby reducing global warming. If the phytoplankton sank to the bottom of the ocean when they died, the carbon dioxide would not return to the atmosphere when the microbes decomposed. 

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