Relative Roles of Surface Fluxes and Strait of Hormuz Exchanges to the Arabian Gulf Salinity Evolution

Abstract

This study investigates the interannual salinity variability in the Arabian Gulf and its relationship with surface freshwater fluxes and lateral water exchanges through the Strait of Hormuz (SoH). Using a 29‐year high‐resolution MIT general circulation model simulation (1993–2021), we quantify basin‐mean salinity changes and their driving mechanisms through a salt and water mass budget framework. The modeled basin‐mean salinity is approximately 0.2 psu lower on average during 1993–1999 than during 2001–2021, indicating an earlier‐to‐later mean‐state contrast within the simulation, superimposed on pronounced interannual variability. Linear regression over 1993–2021 gives a fitted increase of 0.09 ± 0.03 psu per decade, but this slope primarily summarizes the contrast between the earlier and later modeled states rather than indicating persistent linear salinification, and its exact value remains sensitive to conditions during the early simulation years. The cumulative modeled salinity increase reflects the combined effect of persistent net surface freshwater loss (evaporation minus precipitation minus river runoff; E  −  P  −  R ) and compensating water mass exchanges through the SoH. Precipitation variability drives much of the year‐to‐year variations in E  −  P  −  R and associated salinity anomalies, while the higher post‐2000 mean state of E  −  P  −  R reflects contributions from both increased evaporation and reduced precipitation. Annual salinity fluctuations are primarily governed by variability in SoH salt fluxes, while long‐term changes in these fluxes are driven mainly by changes in transport strength (exchanged volume) rather than by changes in the salinity of exchanged waters.