Sea surface salinity changes and trans-basin water vapor transport between the Atlantic and Pacific under CMIP6 abrupt-4xCO2 scenario

Using the latest Coupled Model Intercomparison Projects phase 6 abrupt-4xCO(2) scenario, this study investigates the sea surface salinity (SSS) and hydrological cycle changes in response to global warming in the tropical Atlantic and tropical eastern Pacific. The analysis results reveal the enhancement of the global water cycle and the effect of El Nino-like sea surface temperature (SST) warming. Under global warming, inter-basin water vapor transports increase by about 0.11 Sv (19%) from the tropical Atlantic to the Pacific in response to the rise of the freshwater flux gradient between the two basins. The increase of specific humidity dominates the enhancement of moisture transport (contribution of about 85%), resulting in an SSS decrease in the tropical Pacific and an increase in the tropical Atlantic. On seasonal scales, the increase of the trans-basin SST gradient leads to the enhancement and westward shift of the Walker Circulation in summer and autumn (contribution of 31% in August to 47% in November), further resulting in the precipitation increase and the salinity decrease in the tropical Pacific. Furthermore, the El Nino-like SST warming induces a wind-evaporation-SST feedback in the tropical eastern Pacific. The reduced SST meridional gradient weakens the atmospheric circulation, redistributing the trans-basin water vapor transport. Correspondingly, precipitation (salinity) decreases (increases) in the northeastern Pacific and increases (decreases) in the southeastern Pacific, following the "warmer-get-wetter" mechanism.