Vertical distribution of phytoplankton concentration (Fo) -1, photosynthetic activity (Fv/Fm) - 2 and primary production (by ¹⁴C method) - 3 in sunny day at diurnal station in central region of Baltic sea. A - 9 a.m., B - 11 a.m., C - 1 p.m., D - 4 p.m., E - 7 p.m. Fluorescence was measured with PrimProd fluorometer. Data were obtained during cruise of r/v Oceania, Institute of Oceanology of the Polish AS in september 1995.