Daily variability of chlorophyll a of phytoplankton was studied in the estuarine zone of the Kola Inlet (Barents Sea) during three hydrologic seasons (under conditions of different intensity of light and tidal events). Two types of short-period dynamics of this pigment were discovered. The first period occurred in spring and winter hydrologic seasons with maximum daily fluctuations of chlorophyll a levels at night (the period of complete darkness) and less than minimum velocity of tidal currents. The second period was observed in summer under conditions of maximum influence of tidal events and is characterized by rhythmic fluctuations of pigment concentration during the day according to periods of low and high tides of the tidal cycle.

Keywords: estuarine phytoplankton, chlorophyll a, daily variability, tidal cycle, hydrologic seasons

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