Black Sea anomaly map of Sea Surface Salinity

'''DEFINITION''' The sea surface salinity anomaly in 2019 (SSS') is the time average sea surface salinity (SSS) computed from the reanalysis results in 2019 minus the reference sea surface salinity (SSS), so that 〖SSS'=SSS-SSS. The map of sea surface salinity anomaly is derived from the results of the Black Sea reanalysis (product reference BLKSEA_MULTIYEAR_PHY_007_004). The reference is the time-averaged SSS computed from 1993 to 2014 using the own reanalysis results. This OMI has been discussed in Mulet et al. (2018).

'''CONTEXT''' The Black Sea is a semi-enclosed basin with peculiar characteristics such as a positive net freshwater balance, which is mainly related to the outflow of some of the largest European rivers (e.g. Danube, Dniepr) and high-rate of precipitation which in total exceeds the total evaporation most of the time over the basin (Kara et al., 2008). In addition, an inflow of saltier water originates from the Mediterranean Sea, crosses the Marmara Sea and impacts the Black Sea circulation through the Bosporus Strait (Stanev et al., 2001). The sea surface salinity anomaly is a valuable metric to evaluate the impact of such external forcing on the Black Sea (Mulet et al., 2018). A negative (positive) anomaly means that the sea surface salinity of the analyzed year is fresher (saltier) as compared to the reference period, which may be caused by larger continental runoff and/or precipitation (evaporation) fluxes. Moreover, sea surface salinity changes due to the local variations in ocean dynamics are also not negligible. For instance, the processes induced by the Rim Current and its inherent vortices can locally impact the thermohaline structure in the Black Sea (Kubryakov et al., 2018; Miladinova et al., 2017). The salinity trends are still poorly studied in the Black Sea, although a more recent study by using model numerical simulations found different salinity trends in the water column: surface (negative), upper (weaker negative) and main halocline (positive) (Miladinova et al., 2017).

'''CMEMS KEY FINDINGS''' In 2019, the Black Sea shows a positive sea surface salinity anomaly over almost the entire basin. The highest positive anomalies are found in the south-western basin such as near the coast and between 43°N and 44°N, where they exceed 0.75. On the contrary, negative anomalies are present in the northwestern shelf, which is under the influence of large continental runoff from important rivers: Dniestr, Dniepr and the northern branch of the Danube.