MODERN SPATIAL-TEMPORAL VARIABILITY OF UPWELLING IN THE NORTH-WESTERN BLACK SEA AND OFF THE CRIMEA COAST

Abstract

The processes of development and transformation zones of the wind upwelling in the north-western Black Sea and off the coast of Crimea in the warm season (May-October) are analyzed on the basis of many years data on wind field and the water surface temperature, satellite observations and results of numerical simulation. The presence of seven of the upwelling zones is confirmed, each of which is characterized by a specific spatial-temporal variability of the surface temperature of the water. Coastal upwelling accompanied by lowering the temperature by more than 5 .C in 12 hours most often is observed in the north-western Black Sea (on average 3–4 cases per warm season). Off the southern coast of Crimea upwelling of this type is observed 1–2 times per season. The greatest number of upwellings is recorded in June. Over the past 30 years due to the weakening of the wind, the total number of cases of the wind upwelling in the northwestern part of the Black Sea decreased by about 23%, and in the south-western coast of the Crimea is almost three times. In principle, this favors the development of recreational infrastructure in the region. However, reducing the frequency of occurrence of upwelling is accompanied by a significant increase in temperature of the surface layer in the warm season that leads to an aggravation of the vertical density gradients in the upper layer of the sea and can cause eutrophication of coastal surface waters and near-bottom hypoxia. A rare case of lowering the temperature, covering the entire north-western part of the Black Sea and the coastal areas of the Crimea was analyzed. This example shows that in some areas the horizontal advection (not upwelling) can serve as the main reason for the sharp drop in temperature of the upper layer of the coastal part of the sea.