Seasonal Water Mass Transformation in Sulu and Surrounding Seas

This study aims to describe and reveal ocean system dynamics in Sulu and its surrounding seas. Data were used based on historical in-situ datasets which involve their physical characteristics with temperature and salinity data downloaded from the World Ocean Database (WOD). Sea surface temperature, sea surface salinity, seasonal T-S plots, and caballing coefficient were used to distinguish water-mass types. At the same time, water column stability was analyzed based on the Brunt-Vaisala Frequency (N2). The results revealed that the three areas were influenced by a seasonal variation. The Sulu Sea affected by the SCS and the Pacific Ocean, including local waters from the Philippines. The SCS waters have lower SST (28 °C) and salinity (33.4 psu) compared to other regions. During the South-East Monsoon, the thermocline layer is thicker compared to the North-West Monsoon in the Celebes Sea. Similarly, in the same area, there is a layer that is thicker than the others. There are at least five main water masses in these waters that originate from the SCS and the Pacific Ocean. There are five water-mass types found in the three regions. The most stable area is SCS with a buoyancy value of around 12 cycl/h in a 100-meter depth, and the buoyancy during SEM is more stable than NWM. Finally, WOD updated 2018 is valuable to analyze water mass dynamics, especially using temperature and salinity.