Seasonal Variability of Thermocline, Sound Speed & Probable Shadow Zone in Sunda Strait, Indonesia

The Sunda Strait is an important strait connecting Karimata and Java Seas with the Indian Ocean. The Sunda Strait is one of the busiest International Sea-lane in Indonesian Archipelago (ALKI). That is used for commercial shipping lanes and possibly for the military (submarines) cruise. For submarine operational purposes, a physical oceanographic dataset is needed which consisting of temperature, salinity, and sound speed. This article is analysing the seasonal variablity of thermocline and sound speed, including a shadow zone estimation. The 0.1 deg C gradient is applied for the thermocline layer determination during four seasons data in 2014. The dataset of INDESO Project (daily, 1/12 deg) has been used. In the North-West Season (January), thermocline layer (28 - 13.5 deg C) occurs at 77 - 155 m depth, has a range of 1,542 - 1,504 m/s sound speed. Those reveals shallower (40 - 130 m depth) of the thermocline layer (29 - 15.8 deg C) during the first Transitional Season (April), with the sound speed range 1,541 - 1,511 m/s. During South-East Season (July), the thermocline layer (29 - 15.4 deg C) has been deeper again (65 - 155 m depth), with 1,542 - 1,550 m/s of sound speed. While during the Second Transitional Season (October), the upper limit of thermocline layer (27 - 13.6 deg C) is a little bit shallower (55 - 155 m depth), with the sound speed range of 1,538 - 1,504 m/s. In annual average, the thermocline (29 - 13.6 deg C) in Sunda Strait laying in between an upper limit layer of 40 - 70 m depths and a bottom limit layer of 130 - 155 m depth. Those layers depth are estimated to be a probable shadow zone area with the sound speed range upper limit of 1,542 m/s. and the lower limit of 1,504 - 1,511 m/s.