Black Sea sea surface salinity anomaly (2017)

'''DEFINITION'''

The sea surface salinity (SSS) anomaly in 2017 (SSS') is the average SSS (''SSS'') computed from the reanalysis results in 2017 minus the reference SSS (<SSS>), so that SSS'=''SSS''-<SSS>. The reference is the time-averaged SSS computed from 1993 to 2014 using the own reanalysis results.

'''CONTEXT'''

The Black Sea is a semi-enclosed basin with peculiar characteristics as a positive net freshwater balance, which is mainly related to the outflow from some of the largest European rivers (e.g. Danube, Dniepr) and also depends on important factors such as the evaporation and precipitation rates. The SSS anomaly is a valuable metric to evaluate the impact of such external forcing on the Black Sea. A positive anomaly means that the SSS is saltier than the reference SSS, whereas a negative anomaly indicates a fresher SSS with respect to the reference one. The reference SSS is usually the average SSS calculated from a long period of time, by utilizing model results as reanalysis or observations. The SSS anomalies can provide key information about the SSS trends over time.

'''CMEMS KEY FINDINGS'''

The Black Sea Physics Reanalysis shows a SSS positive anomaly in 2017. The exception is around the northwestern shelf where there are negative anomaly values in the vicinity of the Danube delta and Dnieper river mouth. The predominance of positive anomalies is qualitatively corroborated by the 0 – 10 m layer ARGO measurements, which also captured high values of salinity anomaly in 2017 (not shown).