Influence of Coastal Upwelling on Chlorophyll a Distribution in the Coastal Zone of the Southeastern Baltic Sea in Summer Periods, 2000-2019

Purpose. The study is purposed at obtaining quantitative estimates of coastal upwelling influence on the distribution of chlorophyll a in the coastal zone of the southeastern Baltic Sea during the summer seasons of 2000-2019. Methods and results. Based on data on the frequency and duration of upwelling events for June-August 2000-2019 and chlorophyll a concentrations from multi -sensor satellite observations in the coastal zone of the southeastern Baltic Sea, long-term and monthly average values of the studied parameters were obtained and the influence of upwelling events on the concentration of chlorophyll a in the surface layer of the sea was assessed. The spatial variability of chlorophyll a in the coastal areas is found to be related to the influence of upwelling events. On average, the chlorophyll a concentration decreases by more than 1 mg/m 3 after an upwelling of any duration and in all summer months. The concentration drop is most significant after the upwelling events lasting more than 6 days. Conclusions. Reduced chlorophyll a concentrations (as compared to the pre-upwelling values) are observed in the course of a week after a coastal upwelling event in the southeastern Baltic Sea.