Mediterranean depth-time anomaly map of Sub Surface Salinity

'''DEFINITION''' The Mediterranean Sub-Surface Salinity is the salinity of the model water column from surface down to 1000m depth averaged over the whole basin. The annual subsurface salinity anomaly is derived from the Mediterranean Sea regional reanalysis modelling results of the MEDSEA_MULTIYEAR_PHY_006_004 (Escudier et al., 2020, DOI: https://doi.org/10.25423/CMCC/MEDSEA_MULTIYEAR_PHY_006_004_E3R1) and is evaluated as the average salinity of a given year at a specific depth minus the reference salinity at the same depth, considering as a reference the time-averaged salinity computed from 1993 to 2014 (using the same reanalysis results). A positive anomaly means that the sub-surface salinity is saltier than the reference, whereas a negative anomaly indicates a fresher sub-surface salinity with respect to the reference one.

'''CONTEXT''' The Mediterranean is a semi-enclosed sea connected to the Atlantic Ocean to the west through the Gibraltar Strait and connected to the Black Sea to the east through the Marmara Sea and the Dardanelles strait. Water introduced into the basin through the Gibraltar Strait, the Dardanelles and the rivers is balanced by water lost at the surface due to excess evaporation with respect to precipitation and runoff. The salinity that results from this water balance is characterized by surface values at the Gibraltar inflow ~36.5 PSU and values ~ 39 PSU in the Levantine basin. In this context the sub-surface (0-1000m) annual mean and basin average salinity anomaly evaluated with respect to a reference period (1993-2014) is provided to monitor the salinity temporal and vertical variability. The scientific context of this OMI is proposed in Mulet et al. (2018) in the CMEMS Ocean State Report 2 (von Schuckmann et al., 2018). The changes in the vertical salinity profiles of the Mediterranean Sea are indicators of changes in the hydrological cycle of the basin that is impacted by human activities, especially the river runoff and the precipitation regime.

'''CMEMS KEY FINDINGS''' The Mediterranean Sea reanalysis shows sub-surface salinity anomalies increasing from -0.2 to 0.3 PSU at the end of 2019. Negative anomalies are found before 2005 while after year 2000 the anomaly starts to be positive, continuously increasing in time with larger values achieved in the last years especially in the surface layers between 0-200m thus confirming the basin salinification shown in previous studies (Rixen et al., 2005; Vargas-Yanez et al. 2010; Borghini et al. 2014; Pinardi et al., 2015, Schroeder et al. 2016; Skliris et al. 2018 among the others).