Short-term fluctuations of chlorophyll alpha fluorescence versus diurnal variations of solar radiation in the surface water of the Gdansk Basin
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Measurements of chlorophyll alpha fluorescence accompanied by solar radiation measurements were carried out during two spring cruises in the region of the Gdansk Basin. Chlorophyll alpha fluorescence, similarly to that of chlorophyll alpha concentration in the seawater, showed considerable diurnal variability. The measurements provided statistically significant negative correlation coefficients that indicated that chlorophyll a fluorescence is inhibited as solar PAR and UV radiation intensity increases. The approximate range of radiation intensity that corresponded to a clearly marked decline in chlorophyll a fluorescence and chlorophyll alpha concentration was determined. It was revealed that the decline in chlorophyll alpha concentration in the surface water layer resulted from the photodegradation of chlorophyll alpha as well as phytoplankton grazing. In both cases, the resulting observation was an increase of pheophytine a concentration. The vertical migration of phytoplankton was identified as an additional process induced by high radiation levels.
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R. Magulski, Institute of Oceanography, Division of Marine Chemistry and Marine Environment Protection, Gdansk University, Al. Marszalka Pilsudskiego 46, 81-378 Gdynia, Poland