Copyright © The Oceanographic Society of Japan. Seasonal Variation of Stratification in the Gulf of Thailand

Intensive hydrographic observations were carried out in the western part of the Gulf of Thailand and the east coastal sea of Peninsular Malaysia in September 1995 and April–May 1996. The characteristics of seasonal variation of oceanic condition in that area are discussed basis of an analysis of observed water temperature, salinity and density distributions in these cruises and NAGA cruises (Yanagi and Takao, 1998a). Stratification is most developed in March–May mainly due to large sea surface heat-ing and weak sea surface wind, which weakened until September–October, vanishing in December–January. The horizontal distribution of bottom cold, saline and heavy water masses, which are found during the stratified season, is governed by the tidal mixing and the water depth. Water exchange between the Gulf of Thailand and the South China Sea becomes large in March–May due to a coupled effect of the intensi-fied estuarine circulation and the Ekman transport by the southwest monsoon. May 1996 by M.V.SEAFDEC at 81 stations in the west-ern part of the Gulf of Thailand and the east coastal sea of Peninsular Malaysia (Fig. 1). A CTD (Conductivity, Temperature and Depth profiler) cast was made at each observation station in order to obtain the vertical profiles of water temperature and salinity. Density (sigma-t) is calculated from water temperature and salinity using the usual state equation. The spatial resolution of these observations was finer than that of NAGA Expedition since the NAGA cruises covered 36 to 47 stations whereas the SEAFDEC cruises used 81 stations