Characteristics of the Egyptian Mediterranean water masses during the cold and warm winters

Abstract

         Two winter sets of hydrographic data representing warm and cold winters for 1989 and 1990 respectively were used to study the characteristics of Egyptian Mediterranean water masses. The classification was based on the variations of air and surface water temperatures.
         Four water masses were observed during winter; (i) the surface water mass of temperature 17- 19 °C, salinity maximum 39.0->39.2 occupies the upper 200 m layer, (ii) the Levantine intermediate water mass of temperature 15-17 °C and salinity 38.8-39.0 occupies depths between 200 and 400 m,(iii) a mid-depth water mass lies between 400 an 800 m of temperature 14-15 °C and salinity range 38.75-38 and (iv) the deep water mass of potential temperature range 13.3-13.5 °C, salinity 38.6-38.75 and density ~29.1 σ_t .
         By analyzing the water temperature and salinity distributions, we found that the average surface water temperature are 18.88 °C and 16.73 °C during the warm and cold winters, respectively with an average difference of 2.1 °C. The difference reached the maximum value of 2.32 °C at 50 m depth. It decreases with increasing depth to reach 0.12 °C at 200 m depth. At the depth of 250-500 m, the difference was negative and varied between -0.42 and -0.17 °C. The difference of average salinity at the surface was about 0.07 and decreased to reach 0.03 at 50 m depth. At depth of 100 m and down to 500 m, the difference values were negative and varied between -0.03 and -0.09.
          Vertically, the variations in the water temperature and salinity were observed not only on the surface, but also to a deeper layers (>200 m). The surface layer (0-150 m) represents a water mass of high positive temperature difference (up to 2.5 °C) and low positive salinity difference (~0.06). The intermediate layer showed a nuclei of negative difference (-1.4 °C and -0.2 salinity) in the east- ern side of the study area at depth of 200-300 m.