The June maximum of normalized radiance and its relation to the hydrological conditions and coccolithophorid bloom in the Black Sea

The interannual variability of the seasonal cycle of normalized radiance was studied on the basis of the SeaWiFS ocean color scanner data during the period from 1998 to 2002 under different hydrological conditions in six study regions in the Black Sea. Analysis of the variability characteristics and the accompanying information confirmed the concept about the dominating contribution of the coccolithophorid bloom to the formation of the maximum of the normalized radiance in the middle of June. Arguments are presented in favor of the fact that the appearance of the June radiance maximum is caused by the thermal regime of the sea in the preceding winter period. The radiance maximum reaches the greatest amplitude after cold winters and it remains practically unnoticeable after warm winters. This regularity is caused by the fact that, after cold winters, a sharp shallow seasonal pycnocline is formed, which is a necessary condition for the coccolithophorid bloom. Such a pycnocline is located in the Black Sea at a depth of 10 m. It facilitates the accumulation of various particles in the layer of water- leaving radiance, owing to which the June radiance maximum can be at least partly related to the suspended matter of a noncoccolithophorid origin.