Physical Properties of Seawater in Malacca Strait (Southeast Asia) during Monsoon Seasons

Mansor, K.N.A.A.K.; Roseli, N.H.; Ali, F.S.M., and Akhir, M.F.M., 2023. Physical properties of seawater in Malacca Strait (Southeast Asia) during monsoon seasons. Journal of Coastal Research, 39(5), 921–932. Charlotte (North Carolina), ISSN 0749-0208. Malacca Strait (MS) is a narrow passage in Southeast Asia mainly influenced by the Asian monsoon system. As a busy international maritime route, MS is highly exposed to seawater pollution, harmful algal blooms, and jellyfish blooms. To understand the physical properties of the water column in MS, scientific cruise data were used to examine mixed layer depth, stratification frequency, and water mass distribution during two monsoon seasons (March and August). Results showed that surface water in March is fresher and warmer than in August, whereas the bottom depth in March is more saline and cooler than in August. The mixed layer depth for both months did not exceed approximately 15 m for temperature and salinity, with thermocline and halocline layers observed below the mixed layer depth. The temperature and salinity diagram classified three water masses from the cruise dataset—surface warm water, mixed water, and subsurface water—with the potential density anomaly ranging between about 15.5 and 24 kg/m3. The highest density of water mass, subsurface water, was found only in March at a depth between 54 and 80 m. This cool, high-salinity water is the remaining NE monsoon water mass that settled near the bottom because March is the period of change from NE monsoon to SW monsoon. During this time, winds weaken and solar radiation increases, thus creating stable warm surface water. Strong stratification observed in March prevented mixing between warm surface water and cool bottom water. Meanwhile, August is characterized by a warm SW monsoon; thus, the whole MS is occupied by warmer water. This research presents the variation of physical properties in the water column and reveals the influences of monsoon season on shifts of stratification and water mass distribution.