Comparison of Water Mass Characteristics Between the Indonesian Through Flow Exit Passage and South Java Sea, Indonesia

Eco. Env. & Cons. 26 (April Suppl. Issue) : 2020; pp. (S185-S192) Copyright@ EM International ISSN 0971–765X

Comparison of water mass characteristics between the Indonesian through flow exit passage and South Java Sea, Indonesia

B. Semedi1*, A. Purnomosakti1, D. K. Saputra1, I.B. Wahyono2 and A. Soegianto3*

1Faculty of Fisheries and Marine Science, University of Brawijaya, Malang 65145, Indonesia 2Baruna Jaya Unit, Indonesian Agency for the Assessment and Application of Technology, Jakarta 10340, Indonesia 3Faculty of Science and Technology, Universitas Airlangga, Surabaya 60115, Indonesia

(Received 27 September, 2019; Accepted 10 January, 2020)

ABSTRACT Indonesia’s sea is located between two major oceans, Pacific and Indian Ocean. Indonesian Throughflow (ITF) carries water mass from Pacific Ocean through Indonesia’s sea into Indian Ocean throughout the year. ITF enters Indonesia’s sea from Makassar Strait then water mass is distributed into two passage, west and east passage. Bali’s sea is chosen to represent the ITF west exit passage while South Java Sea is chosen because it directly shares border with Indian Ocean, the final destination of ITF water circulation. The data used in this research was obtained using Baruna Jaya IV Research Vessel on RV Baruna Jaya IV Cruise. Measurements of ocean parameters was conducted using Conductivity Temperature Depth (CTD) instrument in October, 2015 at 36 stations with depth varying until 1000 m. The aim of this study was to determine and identify water mass characteristic at the ITF west exit passage and compare the identified water mass characteristic to the South Java Sea’s water mass to see its resemblances or dissimilarities. The result of this study shows that there were six of Pacific Ocean’s water mass found within the ITF exit passage and five of those were found within the South Java Sea. Pacific Equatorial Water mass with temperature from 6 – 16 oC and salinity 34.5 – 35.2 PSU from North Pacific, Eastern South Pacific Water with temperature varying from 9 – 16 oC and salinity 34.3 – 35.1 PSU, Western South Pacific Water with temperature ranging from 7 – 16 oC and salinity from 34.5 – 35.5 PSU from South Pacific Ocean were found dominant within ITF exit passage and also found dominantly within South Java Sea.

Keywords: Indonesian Throughflow, Water mass, Conductivity temperature depth

Introduction current in Indonesia’s sea that is also well known as Indonesia’s Throughflow (ITF). ITF circulates Indonesia’s sea has a various characteristic due to through Indonesia’s seas throughout the year carry- the natural phenomena that occurs within ing water mass from Pacific Ocean to its final desti- Indonesia’s seas. One of those major phenomenat is nation, Indian Ocean (Sprintallet al., 2003; Gordon, global current circulation that passes through 2001). Indonesia’s sea. Indonesia’s geographic location The ITF occurred due to many factors. In previ- that consist of many islands and connects two major ous studies, Wyrtki (1987) and Hasanuddin (1998), oceans are the main cause of the global circulation specifically mentions that the main cause of ITF cir- S186 Eco. Env. & Cons. 26 (April Suppl. Issue) : 2020 culation is the difference of surface water’s height between Pacific and Indian Ocean. According to Yoga et al., (2014); Rak andWeiczorek (2012), every water mass has its own unique characteristics and variations of ocean parameters such as temperature and salinity. Therefore, it can be used to identify water mass characteristic within Indonesia’s sea. Water mass characteristic is very well affected by water circulation both at the surface and in deeper water column (Rauf, 2007). ITF is an important part of global current circulation that distributed water mass through Indonesia’s sea. Wijaya et al., (2001) Fig. 1. Research’s Sampling Stasions. Yellow circle indi- stated that those regional mixing are usually con- cates sampling stations to represent the West ITF centrated within constricting waters, such as strait. exit zone and the orange circle indicates stations There are several straits that included within the ITF to represent South Java Sea. pathway, for example Makassar Strait, Lombok Strait, Ombai Strait and Lifatomola Straits. South give the whole picture of ocean parameter’s condi- Bali Sea is located strategically at the ITF exit pas- tion within West ITF Exit Zona and South Java Sea. sage. The ITFW that circulates and exits through Figure 1 shown 9 sampling stations were picked to Lombok’s straight into South Bali Sea is assumed to represent the west ITF exit zone and 26 were picked give direct impact into water mass characteristic to represent South Java Sea. within South Bali Sea (Kunarso, 2012; INSTANT, The data used in this research was obtained by 2004, Semedi et al., 2016). In fisheries, water mass direct measurement within the selected sampling characteristic’s information in selected region will points. The measurement was conducted varying be able to help scientist to predict particular fish’s from surface up until 1000 m depth. Vertical profile swimming layer and migration while within to monitor the ocean’s stratification and parameter’s marine’s major, the information provided by water condition including temperature and salinity within mass characteristic will be able to show the indica- the water column was expected to be done by mea- tion of horizontal or vertical water mass mixing. suring the ocean parameters until 1000 m depth.

Materials and Methods Results and Discussion

The methods used in this research was descriptive Vertical profile of temperature as seen as Figure 2A analytic. This method was used to describe and ana- showed us that from surface until depth of 70 m, o lyze the comparison of water mass characteristic temperature was ranging from 27.4 – 23 C. The within selected region. The data used in this re- thermocline layer was seen in 70-200 m deep where o search was obtained in October 2015 during The the temperature declined drastically untill 11 C o Baruna Jaya Research Vessel’s cruise. Ocean’s pa- from 22-11 C. The declining trend of temperature rameters measurement was done by using Conduc- value was seen untill the maximum depth of 1000 tivity Temperature Depth (CTD) of Baruna Jaya m, otherwise within deep layer underneath ther- Unit, Indonesian Agency for Assessment and Appli- mocline layer, the decline trend tend to be slower. cation of Technology, Jakarta. This research took 36 From 400 – 700 m, the temperature was declinging o sampling point, within 6.98-10.11oS and104.75- from 10-7.5 C and from 700-1000 m, the tempera- o 116.40o E to represent the whole West ITF Exit Zone ture was declining from 7.5 – 5 C. Declining trend and South Bali Sea. These 36-sampling point were of temperature value was seen within all water col- selected using stratified purposive sampling meth- umn in offshore section of ITF Exit Zone which was o ods. Suri (2011); Teddi and Yu (2007) explained that located at 113.74- 115.97 E. Sections vertical display stratified purposive sampling is a method to pick a of salinity as seen in Figure 2B shows that salinity sampling point in a research in order describe the was ranging 34.3 – 34.4 PSU on surface. The halo- whole condition or characteristic of a selected object. cline layer was seen in 200-400 m, where the salinity In this case, these 36 sampling points were picked to increased siginificantly from 34.6-34.9 PSU. The Fig- B. SEMEDI ET AL S187

Fig.2: Offshore verticalprofile of temperature (A) and sa- Fig. 3: Mid-shore Sections Vertical Display of Tempera- linity (B) in ITF exit passage ture (A) and Salinity (B) in ITF Exit Passage ure 2B shows that the thickness of halocline layer ing trends. The increasing and decreasing salinity was predicted reaching 200 m. The highest salinity trends within the mid-shore section of ITF west exit value was 34.9 PSU and found within the halocline passage was seen all over the water column in this layer. As the depth increases, in 600-1000 m, salinity section, precisely at 113.91–116.17oE. shows a decreasing value from 34.75 – 34.65 PSU. The condition of temperature’s value within the Vertical profile of temperature in mid-shore sec- near-shore section of ITF exit passage was seen in tion of the West ITS’s Exit Passage can be seen in Figure 4A. The condition as seen in Figure 4A Figure 3A. The temperature’s value as seen in the showed less variation within temperature’s value in figure shows not much difference from the one in near-shore section. From surface to 50 m, the tem- offshore section. Within this section from surface to perature varied from 23-20 oC. Thermocline layer 50 m, the temperature was ranging from 25.3-21 oC. was located in 50 -200 m, where the temperature The thermocline layer was located in 50-200 m deep, decreased until 12.5 oC. Decreasing rate in where the temperature declined drastically from 21- temperature’s value was seen slower within the 11 oC. The declining trend was seen within the layer layer underneath the thermocline layer. From 300- underneath the thermocline layer, only with slower 400 m, temperature varied from 7.5-5 oC. Although declining rate. From 400-700 m, temperature was the temperature’s value showed less variation declining from 10-7.5 oC, and from 700 m to the within the upper and thermocline layer, within 400- maximum depth of parameter’s measurement 600 m deep, temperature showed a slightly different which was 1000 m, the temperature declined from value within the water column. The east water col- 7.5-5 oC. The declining rate of temperature’s value umn of near-shore section in ITF exit passage was seen within all water columns in the mid-shore showed a lower temperature’s value than the west section of ITF exit passage from 113.91–116.17oE. side of the water column. This variation showed Vertical display of Salinity’s in mid-shore section only slight difference in temperature value. ITF exit passage value was seen in Figure 3B. It explained that within mid-shore section of ITF exit passage, the thickness of halocline layer was seen to be thinner. Otherwise, increasing and decreasing rate of salinity’s value within the water column showed similar trends compared to the one in offshore section. From surface to 200 m, the salinity was ranging from 34-34.5 PSU. Halocline layer was see from the depth of 200-400 m in this section. The highest salinity was seen at the value of 34.9 PSU in 400 m depth. Salinity’s value within the layer underneath the thermocline layer showed slow declin- Fig. 4. Nearshore Sections Vertical Display of Tempera- ture (A) and Salinity (B) in ITF Exit Passage S188 Eco. Env. & Cons. 26 (April Suppl. Issue) : 2020

The condition of temperature’s value within the m. This indicates that halocline layer is thinner near-shore section of West ITF exit passage can be within the water column near the ITF exit passage. seen in Figure 4B. From surface until 100 m deep, Salinity’s value within the halocline layer in this sec- salinity ranged from 34.55 – 34.65 PSU. The highest tion varied from 34.8 – 34.9 PSU. salinity value was 34.8 PSU, as seen within the east The condition of temperature within the side of near-shore section in 400-600 m deep, while midshore section of South Java Sea was shown in within the same depth in the west side of water col- Figure 6A. Not many difference shown in the umn, the salinity’s value is around 34-75 PSU. temperature’s trend within midshore section com- Temperature condition within offshore section of pared to the offshore section. Within the upper layer South Java Sea can be seen in Figure 5A while salin- of this section, temperature varied from 26-22.5 oC ity condition within offshore section of South Java and within the themocline layer which was located Sea can be seen in Figure 5B. Temperature varied from 50 – 200 m, the temperature value decreased from 27.2-24 oC on surface until 50 m. Thermocline drastically from 22.5- 12.5 oC. Slow rate of decrease layer was seen in 80- 200 m deep. In this thermocline was shown within the layer underneath thermocline layer the temperature significantly decreasing 11oC layer. The temperature was decreasing from 12.5 oC- from 23-12 oC. The layer underneath the ther- 5oC within the deep layer which was seen from 200- mocline layer shows that decreasing temperature’s 1000 m. value until the depth of 1000 m. The lowest tem- Unlike the temperature’s value within Offshore perature in this section was shown 5.7 oC at 1000 m section, the salinity’s value (Figure 6B) shows a depth. The decreasing trend of temperature’s value more similar thickness within its halocline layer. was seen prevalent within the same depth of water However, in this section, the halocline layer seems column in this section. to be thicker than the one in offshore section. The Unlike temperature, salinity shows a bit of varia- Halocline layer within midshore section was seen tion within its trend in this section. As seen in Fig- for at least 600 m thick in the west side of South ure 5B, salinity’s condition is prevalent, varying Java Sea and gets slightly thinner in the middle and from 34.5 – 34.7 PSU within the upper layer (from east side of South Java Sea. Eventhough there was a surface until 200 m). But the halocline layer shows a difference noticed at the thickness of halocline layer, variation of thickness within the water column in the difference of halocline layer’s thickness within this section. The halocline layer starts to be seen in this section was not vast. the depth of 200 m, and the display shows us that within the west side of water column in this section, the halocline layer seems to be thicker than the east side of the water column. The west side of this section shows at least 400 m of thickness within the halocline layer. While in the east side of this section the thickness of halocline layer only seen for about 300

Fig. 6. Midshore Sections Vertical Display of Tempera- ture (A) and Salinity (B) in South Java Sea Temperature’s condition within near-shore section of South Java as seem in Figure 7A doesn’t show much variation on its trend. The decreasing trend of temperature was seen prevalent within the water column. From surface to 100 m, the tempera- Fig. 5. Offshore Sections Vertical Display of Temperature ture was seen varying around 20 oC. The ther- (A) and Salinity (B) in South Java Sea mocline layer was seen within 100-300 m, where the B. SEMEDI ET AL S189 temperature’s decreasing for 7.5 oC from 20-12 oC. found six of Pacific Ocean water mass type. Those Within the layer underneath thermocline until the Pacific Ocean water mass type are Pacific Equatorial maximum depth, temperature kept on decreasing Water (PEW), Eastern North Pacific Water (ENPW), until 7.5 oC. Western North Pacific Water (WNPW) from North Salinity’s condition within the near-shore section Pacific and Southern Pacific Intermediate Water of South Java Sea is described in Figure 7B. Within (SPIW), Eastern South Pacific Water (ESPW), West- upper layer until the depth of 100 m, salinity varied ern South Pacific Water (WSPW) from South Pacific. from 34.5 -34.6 PSU. With increasing depth, the ESPW were dominantly found at 200-700 m. ESPW salinity’s value was also increasing. From 100 -200 has a characteristic of low temperature (9-16 oC) and m, salinity increases from 34.65 – 34.75 PSU in all high salinity (34.3-35.5 PSU). WSPW was found water column. Halocline layer was started to be dominantly at 200- 800 m. WSPW has a similar seen at the depth of 200 m, while in the middle and characteristic with ESPW, a cold (7-16 oC) and high east side of near-shore section, the halocline layer salinity (34.5-35.5 PSU). PEW, ENPW and WNPW was started to seen at 300 m. Salinity’s value was from North Pacific was also found within the ITF ranging from 34.8 – 34.9 PSU within the halocline exit passage. PEW was the most dominantly found layer of this section. within the ITF exit passage. PEW was found dominantly at 200-800 m. PEW has a characteristic of low temperature (6-16 oC) and high salinity (34.5-35.2 PSU). Besides PEW, North Pacific water mass that was found within the ITF exit passage was ENPW and WNPW. However, none of those were dominant within the ITF exit passage. WNPW has a characteristic of temperature varied from 7-16 oC, and salinity from 34.1-34.6 PSU while ENPW has a temperature varied from 10-16 oC and salinity 34.6 PSU. WNPW and ENPW were only found at 200-250 m deep. Gordon and Fine (1996), on their previous study stated that water mass’ structure within Indonesia’s Sea will highly be affected by the water Fig. 7. Near-shore Sections Vertical Display of Tempera- ture (A) and Salinity (B) in South Java Sea mass transport from Pacific’s Ocean by ITF circulation, specifically within ITF passage. Generally, The analysis of water mass characteristic was there are two water mass type that carried by the performed by matching the result of T-S diagram in ITF circulation into Indonesia’s sea. One is medium both ITF exit passage and South Java Sea with pre- salinity water from North Pacific Ocean and two is vious studies. There are several characteristic of higher salinity water from South Pacific Ocean. Pacific Ocean’s water mass characteristic which di- Hadikusumah (2010) mentioned that those water vided into two categories, North and South Pacific will enter Indonesia’s sea specifically within the Water Mass with its own uniqueness and character- thermocline layer. Sprintalll et al. (2009), on previ- istics. Wyrtki (1961); Wyrtki (1975); Defant (1975) in ous study stated that Indonesia’s Sea is a major con- Radjawane and Hadipoetranto (2014) has catego- nection between Pacific Ocean and Indian Ocean. rized these several Pacific Ocean’s water type, as High Salinity and low temperature water from seen in Table 1 and Table 2. Pacific Ocean’s water South Pacific enter Indonesia’s sea from west pas- mass can be identified based on its parameters’ sage. That water mass circulates within >300 m value, i.e. temperature and salinity. By matching the deep. Tillinger and Gordon (2009) categorized ITF value of temperature and salinity in T-S Diagram of transport into several layers. The first one is surface both ITF exit passage and South Java Sea with pre- layer (0-50 m), then thermocline layer (50-200 m), mid vious study, then it can be identified whether or not layer (200-500 m) and the last is deep layer (500-1000 there were Pacific Water Mass found within ITF Exit m). That research revealed that the ITFW circulates Passage or South Java Sea. the strongest within the thermocline and mid layer. The Analysis of ITF Exit Passage’ T-S Diagram as Within the deep layer, there were found ITFW cir- seen in Figure 8 showed that within the ITF were culated although it was not as strong as within the S190 Eco. Env. & Cons. 26 (April Suppl. Issue) : 2020

thermocline and mid layer. Where within the deep layer there were barely found the ITFW. That thing indicates that within the upper layer, there were no ITF circulation occurs. The identification performed within the South Java Sea since it directly shares border with Indian Ocean. The analysis of Pacific Ocean’s Water Mass characteristic on T-S Diagram of South Java Sea can be seen in Figure 9. It showed that five of water mass that was found within the ITF exit passage were also found within South Java Sea. Sprintall et al., (2009), mentioned that ITF circulation carried water mass from Pacific Ocean into Indian Ocean. The five Pacific Ocean’s water masses are Pacific Equatorial Water (PEW), Eastern North Pacific Wa- ter (ENPW), Western North Pacific Water (WNPW), Eastern South Pacific Water (ESPW), and Western South Pacific Water (WSPW). All five water masses were found under 200 m deep and dominantly at 200-800 m. This indicates that water mass from Pa- cific Ocean circulates through west passage of ITF, exits from Lombok Strait and carried away until it reaches South Java Sea. However, water mass within South Java Sea possess more saline water at Fig. 8. T-S Diagram of Pacific Ocean Water Mass of ITF certain depth. Ffield et al. (2005), explained that Exit Passage when ITFW circulates and enters Indonesia’s sea, the water mass stratified and interact with many within upper layer of the water and there was no regional mixing, especially within a huge strait such Pacific Water Mass mixed within that layer. as Makassar Strait. This regional mixing creates less saline water mass than when it entered Indonesia’s Conclusion sea explained why the water mass within the ITF exit zone had lower salinity water compared to the There were six Pacific Ocean Water Mass found water mass within South Java Sea. Gordon et al. within the ITF exit passage, those are Equatorial (1997) stated that ITFW carried by the ITF circula- Water (PEW), Eastern North Pacific Water (ENPW), tion and enters Indonesia’s sea from a big strait, Western North Pacific Water (WNPW) from North Makassar Strait. Those ITFW circulates through Pacific Ocean and Southern Pacific Intermediate thermocline layer and interact with enormous water Water (SPIW), Eastern South Pacific Water (ESPW), mixing within Makassar Strait. When the ITFW Western South Pacific Water (WSPW) from South leaves Indonesia’s sea, the water mass has become Pacific Ocean. With Pacific Equatorial, Eastern less saline water than when it enters Indonesia’s sea South Pacific Water and Western South Pacific Wa- at the first time. These water then creates a bound- ter dominated within the ITF exit passage and South ary when it met South Java’s water mass. South Java Sea water column. Those dominant Pacific Java’s water has typically more saline water. It ex- Ocean Water mass were categorized into low tem- o plains when compare the T-S diagram in ITF exit perature with temperature varied from 6-16 C lo- o passage and South Java Sea, it can be seen that cated on Pacific Equatorial Water, 7-16 C located on South Java Sea has a higher salinity water and Western South Pacific Water and 9-16 oC located on thicker halocline layer. The T-S diagram of ITF exit Eastern South Pacific Water and high salinity water passage and South Java Sea also displayed that at with salinity varied from 34.5- 35.2 PSU located on <200 m deep, there were no Pacific Water Mass Pacific Equatorial Water 34.3-35.1 PSU located on found in both ITF Exit Passage and South Java Sea. Eastern South Pacific Water and 34.5-35.5 located on That evidently indicates that ITFW did not circulate Western South Pacific Water. There were some simi- B. SEMEDI ET AL S191 larities were found within thermocline layer of ITF References Exit Passage and South Java Sea water mass. 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