Abstract
In autumn 2017, the influence of strong storms and mesoscale physical processes on phytoplankton has been studied in the Black Sea. Data on the taxonomic composition and biomass of phytoplankton, the concentration of chlorophyll-a (Chl), particulate organic carbon, primary production, chemical and physical properties of the environment were obtained using field observations, satellite scanners and two Bio-Argo floats. Different species predominated in cold-water and warm-water areas. In the vast cold-water area formed in the central part of the sea due to strong wind exposure for a month, two diatoms prevailed in the phytoplankton biomass: Pseudosollenia calcar-avis and Hemiaulus hauckii . Three-month observations using satellites and Bio-Argo floats showed that in the upper mixed layer (UML) an increase in Chl during the autumn occurred in a pulse mode in response to severe storms which caused the deepening of the UML. In the warm-water area with depleted inorganic nitrogen, located in the north-eastern part of the sea, coccolithophore Emiliania huxleyi prevailed. Periods with high precipitation were often followed by an increase in the abundance of coccolithophores, which indicates an important role of terrestrial runoff as a source of nutrients. Two different mechanisms increased the phytoplankton biomass and Chl in young (two-week-old) mesoscale cyclonic eddies located within the cold-water area. The rise of the nutricline and wind-induced mixing resulted in pulsed nutrient inputs into the upper layers which stimulated the growth of diatoms and dinoflagellates. At the same time, the uplift of nutricline to a depth of 25–30 m with the daily integrated irradiance of 0.2–1.0 mol photons m −2 day −1 was sufficient to form a strong deep Chl maximum consisting of small flagellates and unicellular cyanobacteria. • Cold-water and warm-water areas determine different prevailing species • A growth of phytoplankton occurs in a pulse mode • Cyclonic eddies stimulate the growth of diatoms and dinoflagellates in the upper layer • Uplift of nutricline to thermocline in cyclonic eddies forms a strong deep chlorophyll maximum • Deep chlorophyll maximum consist of small flagellates and unicellular cyanobacteria
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