Interannual variations of the Black Sea Rim Current


Statement of the main outcome: The general circulation in the Black Sea features a cyclonic gyre encompassing the entire basin (Rim Current), which flows approximately over the continental slope, separating the coastal environment from the open sea. The speed of Rim Current varies from year to year giving an overall measure of the intensity of the circulation. The latter is important for many physical and biogeochemical processes such as the formation of the vertical stratification, replenishment of the Cold Intermediate Layer (CIL), dynamics of mesoscale eddies propagating along the gyre, biogeochemistry dynamics, heat redistribution within the basin, anchovy and other fish distribution, pollution dispersion. The data from satellite altimeters and physical modelling is used to identify the most representative areas where one can get stable estimates of the annual mean speed of the Rim Current for the period 1993–2019. An Ocean Monitoring Index, reflecting the annual state of the cyclonic circulation, referred as Black Sea Rim Current Index (BSRCI), is determined and its interannual variations are studied. The time-series of the BSRCI suggest that the Black Sea Rim current speed varies within ∼30% in the period 1993–2019 with positive trend of ∼0.1 m/s/decade. It is found that the Rim current is in close relation to the regional atmospheric circulation and the mean velocity variation is linked to the wind curl above the basin. This proves that the Sverdrup relation applies to the Black Sea Rim current.
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