The influence of a coastal upwelling event on chlorophyll a and nutrient dynamics in the surface layer of the Gulf of Finland, Baltic Sea
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Temporal variation and distribution of chlorophyll a and nutrients concentration was evaluated on the basis of field observations in August 2006 in the Gulf of Finland. Strong easterly winds in August 2006 generated an upwelling event along the Estonian coast of the Gulf of Finland. It caused a drop of the water-surface temperature and nutrient enrichment of the upper layer. At first, the chlorophyll a declined in the area affected by the upwelled water due to the strong advective transport of the chlorophyll a rich waters towards the northern coast and due to the intensive water mixing and low seed population in the upwelling waters. After stabilization of the upwelling, nutrients from the upper mixed layer were consumed fast: there were no nitrites + nitrates left one week later, and phosphate concentration was under the detection limit 2 weeks later. The smaller phytoplankton size fraction showed faster response to the upwelled nutrients compared with the bigger size fraction, showing the increase in chlorophyll a content already during the stabilization of the upwelling. The increase in chlorophyll a concentration in >20-μm size fraction at stations influenced by upwelling was observed only after the relaxation of the upwelling and formation of stratification.
KeywordsUpwelling Nutrients Chlorophyll a Gulf of Finland Baltic Sea
This study was financially supported by the Estonian Science Foundation (grant no. 6752) and Foundation Innove (grant no. 1.0101-0279). This study was presented as a contributed article at the Bat Sheva de Rothschild seminar on Phytoplankton in the Physical Environment, the 15th workshop of the International Association of phytoplankton taxonomy and ecology (IAP). ESF Programm DoRa and a student scholarship from the Bat Sheva de Rothschild Fund supported financially the participation of Natalja Kuvaldina at this seminar.
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