Field investigation of water mass stratification and variability in the Strait of Hormuz

The Persian Gulf is a shallow basin characterized by high evaporation rates, resulting in the formation of one of the saltiest water bodies in the world. To compensate for the evaporative water loss, a less saline water mass enters the Gulf through the Strait of Hormuz, known as the Indian Ocean Surface Water (IOSW). Due to its high density, the hypersaline Persian Gulf Water (PGW) sinks toward the seabed and exits the Gulf through the deeper layers of the Strait of Hormuz, flowing toward the Gulf of Oman. To identify and characterize the water masses present in the Persian Gulf, Strait of Hormuz, and Gulf of Oman, hydrographic surveys were conducted during the summer and winter seasons of the ۲۱۰۲ and ۲۲۰۱ expeditions aboard the Persian Gulf Explorer. Using CTD profiling, physical and chemical parameters of seawater were measured. Analysis of temperature, salinity, and potential density anomaly across isopycnal layers—surface, intermediate, and deep—along north-south and east-west vertical transects enabled the evaluation of water mass structure and distribution in the region. Results indicate that during summer, surface water mixing is intense due to atmospheric conditions such as the monsoon, and stratification primarily occurs below depths of ۳۰ meters. In contrast, winter stratification weakens, and due to lower temperatures, horizontal layering is observed from the eastern Strait of Hormuz to the western end of the Persian Gulf—marked by increasing salinity and density, and decreasing temperature. The IOSW enters the Persian Gulf through the Strait of Hormuz and propagates along the northern coastline. In summer, cyclonic eddies in the Gulf induce southward flow in several central regions. The PGW is observed in the deep central Gulf during summer, while surface mixing between IOSW and Gulf waters reduces salinity in the upper layers. The summer PGW mass is detectable in the western Gulf of Oman at approximately ۱۰۰ meters depth near the Strait of Hormuz. However, in winter, the inflow into the Gulf weakens due to reduced wind forcing and strong horizontal stratification of salinity and density, which limits the penetration of incoming water.

کلیدواژه ها:

Persian Gulf water mass ، Indian Ocean water mass ، seasonal thermocline ، water stratification ، Strait of Hormuz