Wind impacts on salinity and stratification in the Persian Gulf and on water exchange through the Strait of Hormuz

Abstract The Persian Gulf (PG) is a pronounced inverse estuary characterized by strong evaporation, hypersaline waters, and a reversed asymmetry in water exchange through the Strait of Hormuz, where the annual inflowing volume transport exceeds the corresponding outflow. This study uses a high-resolution three-dimensional hydrodynamic model to quantify wind effects on salinity redistribution, stratification, and high-frequency water exchanges. Wind forcing substantially modifies salinity patterns along the PG’s southern coasts, where downwind (northwesterly Shamal) conditions enhance hypersalinity. The wind-straining response of stratification in an idealized inverse estuary contrasts with that in positive estuaries, showing restratification under upwind and destratification under downwind conditions. In the PG, complex bathymetry and tides obscure this signal. Nevertheless, stronger horizontal density gradients in the wind-forced experiment, particularly under prevailing downwind conditions, promote stronger stratification compared to the no-wind case. This is associated with contrasting stratification responses between the upper and lower estuarine zones of the PG. Under upwind (downwind) wind stress greater than ~ + 0.05 Pa (-0.05 Pa), the Wedderburn number ( $$\:{W}_{e}$$ ) exceeds + 5 (− 5) in the upper estuarine zone, while its absolute value (| $$\:{W}_{e}$$ |) remains mostly below 1 in the lower zone. These $$\:{W}_{e}$$ values indicate wind-controlled residual circulation in the upper PG and density-gradient-driven circulation in the lower PG. Wind forcing more than doubles high-frequency extreme net volume and salt fluxes (exceeding ± 0.6 Sv and ± 22 Sv×psu) compared to no-wind conditions, although the annual mean net fluxes remain nearly unchanged between the wind-forced and no-wind experiments. In both experiments, cross-sectionally averaged horizontal density variance changes in concert with inflowing transport, indicating strong coupling between frontal strength and exchange at the Strait of Hormuz. Furthermore, the annual mean inflowing and outflowing volume transports derived from the high-frequency approach decrease by ~ 70% in the residual framework, which removes tidal and other high-frequency components. These findings highlight wind forcing as a critical, yet previously underappreciated, driver of PG dynamics on synoptic time-scales.