Eastern Mediterranean salinity variation observed by SMAP

One of the saltiest seas, the Mediterranean, experiences significant salinity variations in near surface layers. Satellite sea surface salinity (SSS) from Soil Moisture Active Passive (SMAP) mission indicate a salinification of the eastern Mediterranean Levantine Basin at a rate of psu/year during 2015-2018 that is followed by a freshening tendency. Satellite-observed salinity changes are confirmed by Argo float data and suggest possible changes in properties of the Levantine Intermediate Water. SMAP data suggest that Eastern Mediterranean salinification is coincident with a freshening of the western Ionian Sea. Based on satellite altimetry geostrophic currents, these salinity changes are concurrent with a weakening cyclonic circulation in the Levantine Basin and strengthening anticyclonic circulation in the Ionian Sea. The latter is indicative of the Adriatic‐Ionian Bimodal Oscillation System. It is known that such circulation changes reduce (increase) the transport of fresh Modified Atlantic Water into the eastern Mediterranean (western Ionian Sea), and this is consistent with observed SSS changes. The quality and availability of satellite SSS near the coast can be limited by land contamination. It is shown that absolute SSS retrievals exhibit up to 1psu biases in the eastern Mediterranean. This study’s use of SMAP SSS anomaly mapping instead of absolute SSS illustrates that observed spatial/temporal SSS patterns allow investigation of time variable change in this basin and may augment the existing regional observing system.