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 (2,025Kb)
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6,319,000 Yen (FY1995 1,575,000 Yen)
To evaluate quantitatively cause/effect of global distribution of chlorophyll to physical environments such as ocean water circulation and surface mixed layer, a standard global circulation model is developed and employed. In the steady state of the model with annual surface forcing, equatorial and high latitudinal upwelling areas in the surface layer correspond to high primary productivity areas in the annual mean pigment distribution derived from the satellite ocean color data(CZCS data). Seasonal variations of surface mixed-layer depths (1) in the model and (2) in the in-situ observed temperature data(Levitus, 1982) are compared with seasonal variations of surface pigments from CZCS data. At mid- and high latitudes of the western North Pacific and the North Atlantic, shallowing of the mixed-layer depth from winter to spring largely explains basin-scale features of the spring bloom of phytoplankton in terms of the Sverdrup's(1953) critical depth theory. In the eastern North Pacific and the Southern Ocean the absence of a spring bloom is difficult to explain using the critical depth theory because Sverdrup's(1953) parameters are treated as constants, which in nature vary with physiological and ecological conditions. At northern latitudes the termination of fall bloom corresponds to a deepening in the mixed layer beyond the critical depth. Sverdrup's(1953) critical depth theory is found useful as a first step in examining the general pattern of phytoplankton seasonality. Based on these results, development of global oceanic chlorophyll model, where a numerical ecosystem model is embedded in the present ocean general circulation model, is encouraged for future studies.
Global Circulation Model, Surface Mixed Layer, Seasonal Variation, Chlorophyll Distribution, Bloom