Exploring thermocline and water masses variability in southern South China Sea from the World Ocean Database (WOD)

Study about water characteristics (temperature and salinity) from the World Ocean Database (WOD) was conducted in the area of southern South China Sea (SSCS), covering the area of 0°-10°N, 100°-117°E. From inter-annual analysis, upper layer (10 m) and deep water temperature (50 m) increased from 1951 until 2014. Monthly averaged show that May recorded the highest upper layer temperature while January recorded the lowest. It was different for the deep water which recorded the highest value in September and lowest in February. Contour plot for upper layer temperature in the study area shows presence of thermal front of cold water at southern part of Vietnam tip especially during peak northeast season (December-January). The appearances of warm water were obviously seen during generating southwest monsoon (May-June). Thermocline study revealed the deepest isothermal layer depth (ILD) during peak northeast and southwest monsoon. Temperature threshold at shallow area reach more than 0.8℃ during the transitional period. Water mass study described T-S profile based on particular region. Water mass during the southwest monsoon is typically well mixed compared to other seasons while strong separation according to location is very clear. During transitional period between northeast monsoon to southwest monsoon, the increasing of water temperature can be seen at Continental Shelf Water (CSW) which tend to be higher than 29℃ and vice versa condition during transitional period between southwest monsoon to northeast monsoon. Dispersion of T-S profile can be seen during southwest monsoon inside Tropical Surface Water (TSW) where the salinity and temperature become higher than during northeast monsoon.