Tidal impacts on volume and salt transport through the Strait of Hormuz and on Persian Gulf salinity

Abstract This study uses high-resolution numerical modelling to quantify the impact of tidal forcing on water and salt transport through the Strait of Hormuz (SOH) and its influence on salinity distribution in the Persian Gulf (PG). By resolving high-frequency dynamics, we evaluate exchange flow rates under both tidal and nontidal conditions. Two key findings emerge: (1) Tides significantly enhance mixing within the strait, increasing the salinity of inflowing waters. This reduces the freshening effect of the Oman Sea on the PG and elevates the PG’s mean salinity by over 0.8 psu, thereby strengthening the horizontal salinity gradient between the PG and the Oman Sea. (2) Tidal oscillations more than double the annual mean inflow-outflow rates through the SOH from approximately ± 0.25 Sv in the nontidal model to about ± 0.54 Sv under tidal conditions. Three competing mechanisms dominate the net salt transport at the SOH: (i) Seaward flux from shear dispersion, driven by horizontal salinity gradients; (ii) Minor seaward flux from tidal pumping, resulting from negative covariance between tidal velocity and salinity over annual scales; (iii) Landward advective flux, associated with net landward volume transport, which is typical of inverse estuaries. Tidal forcing enhances the seaward salt flux via shear dispersion. Furthermore, tidal mixing is vigorous throughout the PG, with the advection-to-baroclinicity ratio consistently exceeding 0.5 on a logarithmic scale and surpassing 1 in coastal areas. Tides are a critical driver of horizontal mixing between evaporative, high-salinity coastal waters and fresher, offshore waters, significantly shaping the PG’s salinity distribution.