Quantifying the Contribution of Salinity Effect to the Seasonal Variability of the Makassar Strait Throughflow

The Makassar Strait throughflow (MST) constitutes a significant component of the Indonesian throughflow (ITF) and plays a pivotal role in the interbasin exchange between the Indian and Pacific Oceans. While previous studies have suggested that the buoyancy forcing plays a role in influencing the seasonality of the MST, the quantitative contribution of salinity effect on MST seasonality remains unclear. Here we use the measurements from the Monitoring ITF program and the Global Ocean Physics Reanalysis product to investigate the seasonality of MST and quantify the impact of the salinity effect. We find that the halosteric variability due to the salinity effect contributes to approximately (69.6 +/- 11.7) % of the total seasonal variability of surface dynamic height gradient along the Makassar Strait, and dominates the seasonality of the upper layer MST. The primary drivers for freshwater forcing are horizontal advection through the Karimata Strait and precipitation in the Java Sea. The Indonesian throughflow (ITF) connects the tropical Pacific and Indian Oceans, playing a big role in moving heat and freshwater between them. The Makassar Strait throughflow (MST), which is a major part of the ITF, is important for both regional and global climate systems. Previous studies suggest that the freshwater flux can affect the transport and vertical structure of MST throughout the year. In this study, we used current observations in the Makassar Strait and other high-resolution data to investigate how MST changes with each season, specifically focusing on how salinity changes affect it. The impact of salinity changes on the seasonal variations in MST overwhelms that of temperature changes. Most of the freshwater in the Makassar Strait comes from water flowing through the Karimata Strait, with some contribution from local rainfall in the Java Sea. The Makassar Strait throughflow (MST) shows significant seasonality associated with the along-strait sea surface height gradientHalosteric dynamic height (DH) dominates the seasonal variability of the sea surface DH gradient and MSTAdvection of freshwater from the Karimata Strait and local precipitation constitute the major freshwater forcing for the MST