VERTICAL TEMPERATURE AND SALINITY CHARACTERISTICS AND THEIR RELATIONSHIP WITH WATER MASS DURING THE POSITIVE IOD, NEGATIVE IOD, WEST MONSOON, AND EAST MONSOON SEASONS IN THE MENTAWAI STRAIT

Abstract

The Mentawai Strait is part of the Western Indonesian Waters and is geographically influenced by the interannual phenomena of the Indian Ocean Dipole (IOD) and monsoon. The research location is situated between 2.3°-3.3° North Latitude and 100°-101.5° East Longitude. Conductivity Temperature Depth (CTD) data were used to measure parameters such as depth, temperature, and salinity. The analysis of CTD data utilized T-S diagrams, which depict the relationship between temperature and salinity at various depths. Additionally, ocean current model data were employed to observe the horizontal distribution of ocean currents. The analysis of the T-S diagrams indicated the presence of a thermocline layer at depths ranging between 50 and 150 m. During negative IOD events, the thermocline layer occurred at depths of 92-155 m, which is deeper than during positive IOD events, where it was found at depths of 77-130 m. Similarly, during the west monsoon, the thermocline layer occurred at depths of 92.3-155.8 m, deeper than during the east monsoon, where it was observed at depths of 55.7-109.7 m. The ocean currents in the Mentawai Strait are influenced by changes in the IOD and monsoon patterns. During negative IOD events, the dominant current direction is from the northwest to the southeast, while during positive IOD events, it is from the southeast to the northwest. Similarly, during the west monsoon, the dominant current direction is from the northwest to the southeast, while during the east monsoon, it is from the southeast to the northwest. The characteristics of water masses in the Upper Water layer (0-500 m) in the Mentawai Strait region consist of Benggal Bay Water (BBW), Subtropical Low Water (SLW), South Indian Central Water (SICW), Indonesian Upper Water, and Indian Equatorial Water. As for the Intermediate Water layer, the most dominant water mass originates from the Red-Sea Persian Intermediate Water (RSPIW). Under the conditions of positive IOD, negative IOD, west monsoon, and east monsoon, no significant differences in water mass characteristics were observed.

Keywords: IOD, Mentawai Strait, monsoon, T-S Diagram, water mass.