PHASES OF THE DEVELOPMENT OF THE EXTENSIVE UPWELLING ON THE NORTHWESTERN SHELF OF THE BLACK SEA IN AUGUST 2019 AND ITS IMPACT ON PHYTOPLANKTON
Keywords:
upwelling, phytoplankton, northwestern shelf, Black SeaAbstract
The article presents the results of a study on the development phases of a large-scale upwelling event on the northwestern shelf of the Black Sea in August 2019 and its impact on the hydrological, hydrochemical, and biological characteristics of the marine environment. The study is based on the analysis of satellite data, instrumental observations from the Odesa-Port Hydrometeorological Station, measurements conducted near Cape Malyi Fontan, and laboratory analysis of phytoplankton samples. Changes in sea surface temperature, salinity, sea level, and nutrient concentrations during the period of 1–15 August 2019 were investigated. Particular attention was paid to the role of wind conditions in the formation of the upwelling event. It was established that the development of the upwelling occurred in several phases: preconditioning, active development, and decay. The initial stage was caused by the intensification of northern and northwestern winds up to 9–12 m/s, which led to the offshore transport of surface waters and the rise of cold bottom waters near the eastern and northern coasts. A subsequent shift in wind direction to south–southwestern activated the upwelling of deep waters near the western and northwestern coasts. As a result, the surface water temperature decreased in separate locations by more than 9 °C, and the cold-water zone covered a significant part of the coastal area. Hadrochemical analysis revealed a substantial increase in nutrient concentrations during the active phase of the upwelling: silicon concentrations increased more than tenfold, nitrite concentrations tripled, and total phosphorus increased by 20%, contributing to the intensification of productive processes. A significant impact of upwelling on the phytoplankton structure was also recorded: the number of species increased from 11 to 28–35 and subsequently decreased to 10. The obtained results confirm that upwelling is an important natural mechanism causing short-term but significant changes in the hydrophysical, hydrochemical and biological characteristics of the marine environment by enriching surface waters with nutrients The practical significance of the study lies in the possibility of using the results for forecasting the ecological state of the Black Sea coastal waters and assessing the impact of upwelling processes on the intensification of productive processes.
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