Changes in the Nature of Temperature Anomalies of the Black Sea Surface During the Warming Period of the Late 20^th–Early 21st Centuries

Abstract

Based on the analysis of satellite data from 1982 to 2021 with a spatial resolution of about 0.05° × 0.05°, the total increase in the Black Sea surface temperature was confirmed. Annual temperature averaged over the entire Black Sea rises with the rate of about 0.6°C/10 years. The annual temperature increment due to the linear trend is at a maximum in May–June. In these months of the hydrological spring, the rate of increase in sea surface temperature (SST) is about one and a half times greater than in October–November. For most of the year, the general warming of the surface water layer is not accompanied by a significant increase in the intra-monthly SST variance. Such an increase is observed only in some months of the transition seasons, especially during the hydrological spring, when the absolute magnitude of extreme thermal anomalies and their area significantly increases. The maximum amplitudes of interannual variations of SST are confined to the northwestern part of the Black Sea. Changes in atmospheric pressure and wind fields significantly impact on the spatiotemporal SST structure of the. Long-term trends of driving pressure above the Black Sea indicate an intensification of regional cyclonic activity in the atmosphere (especially pronounced since 2009), which leads to increased generation of the negative SST anomalies of significant amplitude. Such anomalies occur mainly in the warm half-year (especially in May and October) due to the development of wind-driven upwelling. The May and October negative SST anomalies from the range of –(6–5)°C are characterized by maximum areas. Warm anomalies are also most often recorded in May and (to a lesser extent) in October. They are generated by abnormal heat fluxes on the sea surface, including in shallow areas of the shelf and spread to open areas of the Black Sea due to horizontal advection of mainly wind origin. The described patterns of spatio-temporal SST variability and their causes are illustrated by a case-study of extreme thermal anomalies using comprehensive analysis of wind and SST fields of high spatial resolution.