Seasonal Variations of Acoustic Properties in Ropme Sea Area

Abstract

Hydrographic data collected in the periods from 1961 to 1988 are used to investigate sound speed distribution in the Regional Organization for Protection of Marine Environment (ROPME) sea area in the Gulf, during four seasons. The horizontal distributions of the anomaly of the vertically averaged sound speed from 1500 m/s showed a minimum deviation (5-10 m/s) in the area delineated by 22-24°N and 60-62°E, i.e., in Gulf of Oman where the depths exceed 2000 meters. The seasonal temperature variations are reflected on the sound speed changes especially west of Hormuz Strait with shallow depths. The vertical sound speed profiles at deep stations in February, March, May, September, November and December, in the Gulf of Oman, manifested a sound channel at 1500-2000 m depth. In winter, the thermocline layer was not identified west of Hormuz Strait, but in March it starts to develop and was detected in other seasons. In the Gulf of Oman, the thermocline was deeper in winter than in summer. Sound speed was similar in the upper 60 meters. From an acoustic point of view, the basin west of 56°E is considered as a shallow area while the Gulf of Oman is a deep area. Although the thermocline was clear in the shallow part of the study area in summer, the salinity increase with depth cancelled the influence of temperature decrease on sound speed and the profiles became homogeneous.