139736eo.pdf (20MB) - Japan Oceanographic Data Center

PHYSICAL OCEANOGRAPHIC PROPERTIESThe temperature-salinity diagram for the Gulf winter waters (Fig. 6) clearly shows the T-Smaximum associated with the outflowing water in the Gulf of Oman. Surface water of approximately22°C and 36.5%0 enters the inner Gulf and flows northward, cooling to 17-18°C and being greatlymodified in salinity to 40.5%0 as it flows out. The cluster of points of high salinity on the right ofFigure 6 represents deeper outflowing water and also the cool very high salinity water found on thewestern and southern shelves. According to BREWER and DYRSSEN (1983, this line of pointsacross the bottom of the diagram represents the intense (but low capacity) signal of low salinity wateroriginating from the confluence of the Tigris, Euparates and Karun rivers at the delta of the ShattAl- Arab.The surface salinity distribution (Fig. 7a) shows Gulf of Oman water entering and tending toflow northwards along the Iranian Coast. The vertical salinity distribution along the major axis (Fig.7b) shows the Mediterranean-type circulation clearly. The highest deep salinity along this section atStation 2368 is of particular interest. BREWER and DYRSSEN (1985) show that these high salinitywaters form in the shallow area near United Arab Emirates' coast and migrate down slope to augmentthe outflowing waters.The Gulf undergoes wide and rapid temperature changes in response to daily and seasonalcycles of heating and cooling. As with salinities, the highest water temperatures are found in theshallow bays and lagoons where annual temperatures can range from 15°C in winter to 40°C insummer. Even offshore, temperatures can range from 18'C in winter to 36°C in summer.Mixing processes in the Gulf were reviewed by HUGHES and HUNTER (1979) whoshowed, from simple analyses of the limited oceanographic data available, that: a) The time to obtain90% mixing of a contaminant over a water column in the Gulf would be around 16 days (longer insummer, due to the presence of vertical thermal density stratification), and b) Exchange of water in thehorizontal direction is dominated by the residual circulation. Two time scales were estimated for theGulf by HUGHES and HUNTER (1979) in relation to the overall mixing processes. The time for90% flushing of the basin was estimated to be of 5.5 years. They also estimated the time it takes forall the water in the Gulf to come within the influence of the open sea to be days. However, if theinteraction of vertical mixing is included with their estimated residual current, the turnover timeincreases to 2.4 years which corresponds to the value estimated by HARTMANN et al. (1971).TIDES AND TIDAL CURRENTSThe tides in inner Gulf co-oscillate with tides in the narrow Strait of Hormuz, while tides inthe Gulf of Oman co-oscillate with those in the Arabian Sea. Usually the Gulf and the Strait ofHormuz are treated as a coupled system for tidal computations. The range of tides in the Gulf isgreater than 1 m (LEHR, 1984), and exceeds 3 m at Shatt-al-Arab, These large amplitudes causestrong tidal currents which commonly exceed 0.5 m s-1 at maximum ebb or flood. The tide appears toprogress up along the Iranian coast from the Strait of Hormuz and down the coast of Saudi Arabia.The dimensions of the Gulf are such that resonance amplification of the tides can occur (HUGHES andHUNTER, 1979).M2, S2 and Kl tidal constituents (Fig. 8),together with O1 tides, are the four important tidalconstituents in the Gulf. As can be seen, the semi-diurnal constituents have two amphidromic points,one in the northwestern part of the Gulf and the other in the southwestern part. The IC2 and O1constituents have a single amphidromic point almost in the middle of the Gulf. In fact, the tides in theGulf are complex, consisting of a variety of tidal types (Fig. 9), with areas semi-diurnal [S = (M2+ S2)/( K, = 01)