Temperature, salinity, dissolved oxygen and water masses of Vietnamese waters

Abstract

During April and May 1999, An MV SEAFDEC cruise was carried out in Vietnamese waters for the SEAFDEC Interdepartmental Collaborative Research Program on Marine Fishery Resources. Data on temperature, salinity and dissolved oxygen concentration of water in the area were collected using the Integrated CTD instrument. The survey period was in April to May which is the transition period between the Northeast monsoon to the Southwest monsoon, the feature from the study seem to mix under the influence of both monsoon seasons. The Northern part of the survey was still under the influence of the Northeast Monsoon as shown by the lower temperatures and higher salinity water of water along the coast from Da Nang to Nha Trang than those off shore. In the southern part of the area, the Southwest monsoon started to prevail as shown by the occurrence of weak upwelling off the Nha Trang coast, the shallow mix layer and the covering of mixed layer of the outer Gulf of Thailand station by the Thailand Gulf mixed layer water. The runoff from the Red and the Mekong River also plays an important role in the characteristics of the water in the study area, as shown from the distribution of low salinity and low oxygen off coast near the river. There was an intrusion of subsurface water (10-15 m) from off the Mekong River station to the subsurface water of station no.56 and 57 in the outer Gulf of Thailand. Temperatures between 29.5-30°C and salinity of about 33.2-33.5 PSU characterize the water. Six water masses, Continental shelf water, Open sea water, Maximum salinity water, Seasonal thermocline water, Permanent thermocline water and Deep water, were found during the survey period.