Assessment of oceanographic characteristics and water mass exchange in the Persian Gulf and Gulf of Oman

Abstract

Physical oceanography of the Persian Gulf (PG), Strait of Hormuz (SH), and Gulf of Oman (GO) waters is poorly understood, necessitating more extensive and long-term studies. The main goal of this research is to comprehend the oceanographic properties and water mass exchange in this region. The study evaluates the range and patterns of the changes in physical characteristics (salinity (S), temperature (T), and depth (D or pressure, P)) and structure, mixing and stratification, and circulation of water in the PG, SH and GO. The findings revealed that the maximum recorded sea surface temperature in the PG exceeded than that in the GO during the summer. Seawater temperature in the PG decreased from east to west in the winter. The maximum sound speed values were in the surface layer during the summer (approximately 1557.5 m/s). The maximum salinity gradient and winter halocline were found between depths of 40 and 60 m. The vertical structure of seawater indicates the formation of strong thermal and density stratifications in the summer. The Richardson Number (R_i No.) in the SH ranged from ${0.5<R}_{i}No.<0.65$ in the summer and it varied between ${0.03<R}_{i}No.<0.15$ during the winter. A dense water mass with a salinity more than 40 psμ (originating from the PG) was found below 150 m depth in the southwestern part of the GO. The stability and layering of the water column in the SH are under effect of the two-layer currents and the movement of water masses between the PG and GO. The static stability number (E) of the water column in the eastern part of the PG varied in the range of $3\times {10}^{-4}<E<6\times {10}^{-4}$ during the winter, and between $12\times {10}^{-4}<E<16\times {10}^{-4}$ in the summer. The maximum amount of the density anomaly occurs in the deep areas of the PG during the summer. During the winter, a two-layered water structure forms in the central areas of the SH. Horizontal and vertical gradients of the salinity and density facilitate the exchange of water masses between the PG and the GO through the SH. The average flushing time (Residence Time, T_Residence) of the PG is 1.82 years. The findings of the study offer an observational evaluation of the water mass exchange, seawater parameters, stratification, and variations in sound speed. It is recommended continuing the study with additional sampling stations, particularly in the southern part of the PG, and conducting flow measurements in the SH.