The Effects of the Indonesian Throughflow, River, and Tide on Physical and Hydrodynamic Conditions During the Wind- Driven Upwelling Period North of the Aru Islands

Abstract

A three-dimensional baroclinic nonlinear numerical model—the Hamburg Shelf Ocean Model (HAMSOM)—was applied to investigate the effects of the Indonesian throughflow (ITF), river runoff, and tidal forcing on circulation during the southeast monsoon period (July 2004) north of the Aru Islands by conducting different sensitivity runs. It was found that the Ekman transport over the continental slope of the Sahul Shelf was the main factor that causes upwelling north of the Aru Islands, and this was suggested to be one of the main factors behind the surface water in the research area being relatively colder and saltier than the surrounding waters. The influence of South Pacific Subtropical Water (SPSW) on the surface water was indicated by the high surface salinity of waters within the internal salinity maximum layer. The results also suggested that onshore subsurface currents over the slope were induced not only by offshore surface currents over the slope but also by the ITF. By considering the eastern ITF route, river runoff and tidal forcing were also found to contribute significantly to the erosion of the salinity maximum (approx. 0.25) within the Halmahera Sea, thereby reducing sea surface salinity north of the Aru Islands. Furthermore, it was proposed that river runoff from the western coast of Papua Island contributed to intensified cross-shelf circulation over the continental slope. These conditions were related to enhancing vertical viscosity forces in the surface waters induced by stronger stratification as an impact of river inclusion in the simulation.