Salinity trends and mass balances in the Mediterranean Sea: revisit the role of air-sea freshwater fluxes and oceanic exchange

Abstract. Understanding the drivers of salinity and mass variability in the Mediterranean Sea is critical for assessing regional climate impacts and interpreting long-term water cycle changes. Although previous studies have closed the Mediterranean's mass and salinity budgets within uncertainty ranges, the relative contributions of key boundary fluxes – surface freshwater fluxes (evaporation minus precipitation minus runoff) and Gibraltar exchange – remain unclear. Here, we analyze the Mediterranean budgets from 2003 to 2017 using the ECCO v4r4 ocean state estimate. Our results show that surface freshwater loss, averaging 1.80 ± 0.10 Sv, dominates salinity variability, while the net Gibraltar exchange contributes a smaller, yet essential, salt input of 0.30 ± 0.20 Sv. Despite the saltwater inflow, the Mediterranean exports salt through the strait at −1.48 ± 0.20 Sv due to density differences between Atlantic Water (AW) and Mediterranean Outflow Water (MOW), leading to an overall salinity increase of 0.29 ± 0.09 Sv over the 15-year period. These results are consistent with observed Mediterranean salinification trends and underscore the dominant role of surface evaporation in shaping the basin's long-term evolution. This study provides a physically consistent, basin-integrated benchmark for interpreting Mediterranean water cycle changes under continued climate forcing.