*4.2. Circulation*

The surface mean circulation is shown in Figure 10 as monthly means for 2019. Considering the poor availability of observations, a robust validation exercise is extremely difficult, thus the main features emerging from the annual monthly means are described in detail with respect to those extensively described in [28–31].

**Figure 10.** Surface currents in 2019: monthly means from Jan to Dec 2019. The reference month and depth are written on the top of each panel. Main structures: (1) Rim Current, (2) Western Gyre, (3) Central Gyre, (4) Batumi anticyclonic eddy, (5) anticyclonic coastal eddy, (6) Caucasus anticyclonic eddy, (7) cyclonic coastal eddy, (8) Kerch anticyclonic eddy, (9) Sevastopol anticyclonic eddy.

The Black Sea surface dynamics is characterized by a main cyclonic gyre, the Rim current, encompassing the basin and a variety of mesoscale eddies along the coast, some of them quasi-stationary. BSFS captures most of the particular dynamical structures in the basin, such as the Rim current, which persists over 2019, and small-scale structures such as coastal anticyclonic eddies, which appear along the Russian–Georgian coastline (one quite intense in February and progressively weaker in March) and coastal cyclonic eddies, which are much more intermittent over the year and weak). The Batumi Gyre, located near the Georgian coast, forms in April and lasts until June, when the circulation in that region is fragmented in more unstable and weak eddies until its regeneration in August–September. Progressively towards the southwestern region, small coastal eddies become part of the Rim current. On the Turkish coastline, cyclonic eddies like the one in the area of Trabzon (January–February; November–December) coexist with anticyclonic eddies, as in the Synop area (June–October). In the area between Istanbul and Burgas—the Bosporus region—an anticyclonic eddy appears from October to December. Close to the Danube, coastal currents are quite well captured by the model, then going further towards the continental slope (30◦ E–32◦ E and 44◦ N–45◦ N) the Sevastopol anticyclonic gyre starts in May (very weak), becoming stronger in November and December.
