GLOBAL VERIFICATION OF CRITICAL DEPTH THEORY FOR PHYTOPLANKTON BLOOM WITH CLIMATOLOGICAL IN-SITU TEMPERATURE AND SATELLITE OCEAN COLOR DATA

An investigation is made of the global relationship between seasonal v ariations of the surface mixed-layer depths derived from monthly clima tological hydrographic data and seasonal variations of the surface pig ments from monthly satellite ocean color data. At middle and high lati tudes 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 Sverdr up's critical depth theory. In these areas the spring bloom occurs fro m middle to high latitudes along with the increase of insolation from winter to spring. In the eastern North Pacific and the Southern Ocean the absence of a spring bloom is difficult to explain using the critic al depth theory because Sverdrup's parameters are treated as constants , which in nature vary with physiological and ecological conditions. A t northern latitudes the termination of fall bloom corresponds to a de epening in the mixed layer beyond the critical depth. Sverdrup's criti cal depth theory is found useful as a first step in examining the gene ral pattern of phytoplankton seasonality.