Decadal Changes of Hydrographic Structure and Water Masses of the Red Sea

This paper provided a comprehensive analysis of Red Sea hydrographic characteristics, including temperature, salinity, and potential density, in the different seasons by the horizontal and vertical distributions over seven decades from 1951 to 2020. From the spatial distributions, maximum sea surface temperatures exhibited fluctuations, with the highest values observed in the first two decades (1951–1970) and the last decade (2011–2020) in winter, spring, and autumn. In summer, maximum sea surface temperatures peaked in the 2001–2010 decade. Mean water temperatures ranged between 24.7 °C to 25.8 °C in winter, 26.5 to 28.6 °C in spring, 30.1 °C to 31.6 °C in summer, and 27.7 °C to 29.3 °C in autumn across all decades. The salinity and potential density have the highest maximum values in the last decade (2011–2020) across all seasons, which can be related to higher values of remote sensing estimates. Two water masses are observed in winter and spring: Red Sea Surface Water (RSSW) and Red Sea Deep Water (RSDW). In summer and autumn, three water masses were observed in the southern part: RSSW was characterized by a high potential temperature, low salinity, and low potential density. The intermediate water mass that intruded into the Red Sea from the Gulf of Aden in the last two seasons extended to 17 °N and disappeared in the northern part due to vertical mixing. It is characterized by low salinity. The RSDW is identified by low temperature of 21.7–21.9 °C, high salinity of 40.32–40.79, and high density of 28.30–28.75.