Inter-Annual Seasonal Variations in the Seawater Thermohaline Structure in the Northern Gulf of Aqaba, Red Sea

Temporal and spatial variations of seawater temperature and salinity were investigated at three stations in northern Gulf of Aqaba for six years May 1997-April 2003. The results showed that, thermal stratification characterized the upper water column during summer (May-December). The strongest stratification appeared in August exceeding 250 m. Mixing conditions characterized the winter-spring seasons (January-April), which exceeded the deepest measurement point (450 m). Composite variations with time in the stratification depth during summer and the mixed layer depth during the winter-spring season fitted an exponential association. Both the stratification build up and erosion (mixing deepening) rates were relatively high ( ~ 3.5 m.day -1 ) at the beginning of their respective seasons. The processes slowed down significantly late in the season reaching 0.24 and 0.52 m.day -1 for building and erosion, respectively. An interesting phenomenon of higher salinity water overlaying lower salinity water occurred clearly during summer. Local evaporation and lower salinity water carried by the thermohaline currents in intermediate waters from the Red Sea are the most likely reasons of this phenomenon. The inter-annual salinity variation in the upper 450 m was not significant and ranged only between 40.12 and 40.75 PSU, while the temperature variation was relatively high and ranged between 21.02-27.99 o C. This indicates that the thermodynamic processes in the seawater of the Gulf were mainly controlled by temperature, whereas salinity played a minor role. No significant inter-annual differences in the upper 300 m potential temperature, salinity, and potential density were detected among the three study stations at the northern Gulf of Aqaba.