ASGHAR PISHGAHI - MSc.,Physical Oceanography,KUSTEM, Malaysia; BEng., Mechanical Eng.,Azad Univ.,Iran
MAGED MARGHANY - PhD in Environmental Remote Sensing ; MSc. in Physical Oceanography, UPM, Malaysia

In order to identify the water mass, a plot of temperature versus salinity data, from near the surface to the bottom or T-S diagrams can used[1],[4],[5]. This powerful analytical technique was introduced into physical oceanography by B. Helland-Hansen in 1916. In the 1930s the T-S method was extensively used to identify various water masses in the world ocean [9]. Excellent generalization was made by Svrdrup . Johnson and Fleming(1942) to describe layering of water masses that common vertical salinity and temperature distribution , as denoted by their T-S curves [9] also can say each water mass can be identified on the basis of temperature and salinity values at various subsurface depths(pressure).each water mass can be identified by a line that converges to a common point[2]. Saadon and Alejandro (1996) reported that during the northeast monsoon seasons there are two different water masses with lower temperature and salinity than during the south west monsoon.Marghany and Pishgahi (2004) made a study about water masses properties along coastal water of kuala Terengganu . they reported, in general there are two water masses below surface to mid of depth. Pishgahi and Marghany (2004) studied about water masses in south china sea off Pahang .They reported that there are four water masses in that study area ,two water masses inshore and two water masses offshore during pre monsoon. The onshore water masses have a low salinity than offshore because the water discharge from mouth river of Pahang river generate onshore water masses. The aim of this investigation is to study the seasonal water mass variations , pre monsoon and post monsoon ,in South China Sea , by using 2 series data such as temperature , salinity and density or sigma_t (σt) observed by sampling.