Gulf of Oman
Gulf of Aden
The hydrographical conditions in the Gulf of Oman during the two survey periods, summer 1979 (July-August) and winter 1981 (January-February) appear from Fig. 22-23. In the summer the surface water was characterized by high temperature stratification with a thermocline at about 25 m. The stratification of the watermasses is clearly controlled by the temperature with very little stratification of the salinity distribution in the surface watermasses. In winter 1981 the surface water was mixed down to 100 m on all three sections in the central part of the Gulf. The watermasses in the southern part of the Gulf along the continental slope of the Sultanat of Oman are influenced by watermasses that most probably originates from the Persian Gulf. This was observed in both surveys. In summer 1979 a core of water with high salinity was observed at section III (Fig. 22 C) at a depth between 150-250 m and at section II at about 175-300 m close to the continental slope. In winter 1981 the core of this watermass was observed at about the same depths and positions (Fig. 23).
Fig. 22A. Hydrographical sections in the Gulf of Oman. August 1979. A: Section I
Fig. 22B. Hydrographical sections in the Gulf of Oman. August 1979. B: Section II
Fig. 22C. Hydrographical sections in the Gulf of Oman. August 1979. C: Section III
Fig. 23A. Hydrographical sections in the Gulf of Oman, January-February 1981. A: Section I
Fig. 23B. Hydrographical sections in the Gulf of Oman, January-February 1981. B: Section II
Fig. 23C. Hydrographical sections in the Gulf of Oman, January-February 1981. C: Section III
The distribution of the oxygen content of the watermasses in the Gulf of Oman followed that of the temperature. The highest gradients were observed in the thermocline in both survey periods (Fig. 22-23). In summer 1979 water with oxygen concentrations lower than 0.5 ml/l was observed below 100 m on section I, and at about 400 m on section II and III. In winter 1981 oxygen minimum watermasses were found at 100-250 m on section I and cores of watermasses with low 02 content at 150-200 m and 200-350 m on section II and on section III below 350 m.
The hydrographic features of the Gulf of Aden during the two survey periods are presented in Figs. 24-25. The surface watermasses were characteristic for the two seasons. During summer 1979 we observed the thermocline in the upper 50 m, varying in depth due to the current systems in the Gulf (Fig. 24). In winter 1981 the upper 100 m, was characterized by unstable mixed watermasses, except for the central part of the Gulf where we observed a core of surface water with higher temperature and salinity. The thermocline was observed at about 100 m (Fig. 25).
The deep watermasses in the southern part of the Gulf was most probably influenced by currents from the Red Sea. A core of watermasses with high salinity (>36,5‰) was observed at 250 m decending to more than 500 m on section I in summer 1979 (Fig. 24). In winter 1981 a core of watermass was observed in the same section (I) at about 400 m (Fig. 25). Oxygen minimum layers were found in summer 1979 at about 100-150 m on section I and II. In 1981 oxygen minimum layers were found in the Gulf of Aden at about 200 m.
Fig. 24A. Hydrographical sections in the Gulf of Aden. August 1979. A: Section I
Fig. 24B. Hydrographical sections in the Gulf of Aden. August 1979. B: Section II
Fig. 25. Hydrographical section in the Gulf of Aden. February 1981.
