Eastern Mediterranean salinification observed in satellite salinity from SMAP mission

Abstract

Abstract One of the saltiest seas, the Mediterranean, experiences significant salinity variations in near surface layers. Satellite sea surface salinity (SSS) data obtained using Soil Moisture Active Passive (SMAP) mission indicate steady salinification of the eastern Mediterranean Levantine Basin at a rate of ~0.14 psu/year during 2015–2018. Satellite-observed salinity changes are confirmed by Argo float data and suggest possible changes in properties of the Levantine Intermediate Water. Eastern Mediterranean salinification often coincides 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 L-band (1.41 GHz) SSS estimates near the coast can be limited by land contamination. It is shown that absolute SSS retrievals exhibit up to 1 psu biases in the 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 augment the existing regional observing system.