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

Abstract

A general increase in the surface temperature of the Black Sea has been confirmed based on an analysis of satellite data from 1982 to 2021 with a spatial resolution of about 0.05° × 0.05°. The annual mean temperature increase is about 0.6°C/10 years. The annual temperature increase due to a linear trend is maximum in May–June. During these months of hydrological spring, the rate of increase in sea surface temperature (SST) is approximately one and a half times greater than in October–November. During most of the year, the general warming of the surface water layer is not accompanied by a significant increase in the intramonthly SST variance. Such an increase is observed only in some months of transition seasons, especially during the period of hydrological spring, when the absolute value of extreme thermal anomalies and their area increase significantly. The maximum amplitudes of interannual SST variations are confined to the northwestern part of the Black Sea. Changes in the fields of the atmospheric pressure and wind have a significant impact on the spatiotemporal structure of SST. Long-term trends in the surface pressure over the Black Sea indicate an intensification of regional cyclonic activity in the atmosphere (especially pronounced since 2009), which leads to the increased generation of negative SST anomalies of significant amplitude. Such anomalies occur mainly in the warm half of the year (especially in May and October) due to the development of upwellings of wind origin of various types. In May and October, negative SST anomalies in the range of ‒(6–5)°С are characterized by the maximum areas. Warm anomalies are also most often recorded in May and (to a lesser extent) in October. They are generated by anomalous heat fluxes on the sea surface, including those in the shallow areas of the shelf, and spread to open areas of the water basin due to horizontal advection, predominantly of wind origin. The described patterns of spatiotemporal SST variability and their causes are illustrated by a comprehensive analysis of wind and SST fields of high spatial resolution during the development of extreme thermal anomalies.