Interestingly, large vertical excursions of isotherms from depths as deep as 700 m to shallower levels are noticed at the southern latitudes. The theta-S structure at the stations between 50N and the equator clearly shows the presence of three water masses in the upper 450 m followed by a bottom water mass below depths of 3500 m. The subsurface low salinity water mass (34.75 PSU) is located at 24.0 sigma-theta around 130 m at 50 N. The salinity of this water mass increases gradually towards the equator. Interestingly, intrusion of low salinity water mass around 26.0 sigma-theta is noticed at 2. 50S. While the saline near surface water has its origin in the Arabian sea and flowing towards east, the source of less saline subsurface waters at depths of 130 m deserves explanation and further exploration. Towards this, the vertical distributions of nutrients and oxygen are examined to find a clue. This has shown those higher silicates, phosphates and oxygen also characterize the above less saline waters. This suggests that flow into this region is associated with the run-off or fresh water discharge. The flows through the Bay of Bengal having the origin in the Andaman Sea deserve a revisit. Possibly the water from Malacca Straits through the NEC flowing from east to west during northern winter season could also be a candidate. However, the presence of high salinity waters at the near surface depths indicates the weakening of the NEC in the upper 100 m by January (eastern transect) due to weakening of the northeasterly winds in this region. The surface circulation also supports the weak westward flowing NEC. The flow between 30N and 10S is mainly towards southwest and tends to become westward at the western transect (south of Sri Lanka). Between 10S and 5S, an eastward flow associated with ECC, which turns northeastward east of 85E can be seen. In this region, the near surface high salinity (35.4 PSU) water mass centered at 23.0 sigma-theta is brought in towards east by the ECC that prevails during that prevails during the northem winter season. This ECC brings with it the high salinity waters of the Arabian Sea towards east.. Two acoustic paths identified by the researchers at CSIRO. Hobart & N.I.O, Goa emanating from a point source situated off Pt. Leeuwin, southwest Australia, reach the Indian Ocean shores - Madras and Southern Peninsular India. In order to obtain and select suitable experimental site(s) for better signal reception utilizing Geodesic path and refracted geodesic path, algorithrns were developed. Ray trajectories for a range-dependent has been worked out apart from travel tirne and signal strength estimations. The climatic data collected and processed at standard depths available at one degree intervals and the CTD and XBT profiles taken along Madras-Perth-Madras transects were used for calibration of the geodesic acoustic paths connecting the Indian shores to southwest Australia which is crucial for the deployment of any equipment for long term monitoring. The ray computations for different angles of emergence have been carried. From this analysis it was evident that the average travel time difference is +0.4s approximately amounting to a temperature fall by 0.0375 0 C over the entire water column transgressed by the acoustic rays. * Analysis of climatic temperature, salinity fields, sound speed and sound channel parameters enabled identification of regions of significant variations. * Analytical form of sound speed profile revealed wide deviations in the thermocline. * Reference sound speed profiles constructed region-wise and season-wise to examine the order of expected variability in the north Indian Ocean.
