Identification of thermal front dynamics in the northern Malacca Strait using ROMS 3D-model

The thermal front in the oceanic system is believed to have a significant effect on biological activity. During an era of climate change, changes in heat regulation between the atmosphere and oceanic interior can alter the characteristics of this important feature. Using the simulation results of the 3D Regional Ocean Modelling System (ROMS), we identified the location of thermal fronts and determined their dynamic variability in the area between the southern Andaman Sea and northern Malacca Strait. The Single Image Edge Detection (SIED) algorithm was used to detect the thermal front from model-derived temperature. Results show that a thermal front occurred every year from 2002 to 2012 with the temperature gradient at the location of the front was 0.3 °C/km. Compared to the years affected by El Niño and negative Indian Ocean Dipole (IOD), the normal years (e.g., May 2003) show the presence of the thermal front at every selected depth (10, 25, 50, and 75 m), whereas El Niño and negative IOD during 2010 show the presence of the thermal front only at depth of 75 m due to greater warming, leading to the thermocline deepening and enhanced stratification. During May 2003, the thermal front was separated by cooler SST in the southern Andaman Sea and warmer SST in the northern Malacca Strait. The higher SST in the northern Malacca Strait was believed due to the besieged Malacca Strait, which trapped the heat and make it difficult to release while higher chlorophyll a in Malacca Strait is due to the freshwater conduit from nearby rivers (Klang, Langat, Perak, and Selangor). Furthermore, compared to the southern Andaman Sea, the chlorophyll a in the northern Malacca Strait is easier to reach the surface area due to the shallower thermocline, which allows nutrients in the area to reach the surface faster.