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Abstract 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. 

Abstract Multidecadal variability of the Indonesian Throughflow (ITF) is crucial for the Indo-Pacific and global climate due to significant interbasin exchanges of heat and freshwater. Previous studies suggest that both wind and buoyancy forcing may drive ITF variability, but the role of precipitation and salinity effect in the variability of ITF on multidecadal time scales remains largely unexplored. Here, we investigate the multidecadal changes and long-term trend of the ITF transport during the past six decades, with a focus on the role of precipitation and salinity effect. The diverse datasets consistently indicate a substantial upward trend in the halosteric component of geostrophic transport of ITF in the outflow region at 114°E during the six decades. We find that the meridional differences of the salinity trend in the outflow region explain the increasing trend of the halosteric component of ITF transport. On a larger scale, the tropical western Pacific Ocean and Indonesian seas have experienced significant freshening, which has strengthened the Indo-Pacific pressure gradient and thus enhanced the ITF. In contrast, the equatorial trade wind in the western Pacific Ocean has weakened over recent decades, implying that changes in wind forcing have contributed to weakening the ITF. The combined effect of strengthened halosteric and weakened thermosteric components has resulted in a weak strengthening for the total ITF with large uncertainties. Although both the thermosteric and halosteric components are associated with natural climate modes, our results suggest that the importance of salinity effect is likely increasing given the enhanced water cycle under global warming. 

Abstract. Over the past decade, our understanding of the IndianOcean has advanced through concerted efforts toward measuring the oceancirculation and air–sea exchanges, detecting changes in water masses, andlinking physical processes to ecologically important variables. Newcirculation pathways and mechanisms have been discovered that controlatmospheric and oceanic mean state and variability. This review bringstogether new understanding of the ocean–atmosphere system in the IndianOcean since the last comprehensive review, describing the Indian Oceancirculation patterns, air–sea interactions, and climate variability.Coordinated international focus on the Indian Ocean has motivated theapplication of new technologies to deliver higher-resolution observationsand models of Indian Ocean processes. As a result we are discovering theimportance of small-scale processes in setting the large-scale gradients andcirculation, interactions between physical and biogeochemical processes,interactions between boundary currents and the interior, and interactions between thesurface and the deep ocean. A newly discovered regional climate mode in thesoutheast Indian Ocean, the Ningaloo Niño, has instigated more regionalair–sea coupling and marine heatwave research in the global oceans. In thelast decade, we have seen rapid warming of the Indian Ocean overlaid withextremes in the form of marine heatwaves. These events have motivatedstudies that have delivered new insight into the variability in ocean heatcontent and exchanges in the Indian Ocean and have highlighted the criticalrole of the Indian Ocean as a clearing house for anthropogenic heat. Thissynthesis paper reviews the advances in these areas in the last decade.