Effects of High-Frequency Flow Variability on the Pathways of the Indonesian Throughflow

Previous studies have shown the presence of strong mesoscale eddy activities in the Indonesian Seas and their influence on the transport and water mass properties of the Indonesian Throughflow (ITF), a mean flow from the Pacific Ocean to the Indian Ocean through the Indonesian Archipelago. This study explores the effects of these eddy activities, or high-frequency flow variability (HFFV), on residence time and pathway of the ITF by conducting Lagrangian particle tracking experiments using a velocity field from an eddy-resolving ocean general circulation model. Particles are released at key locations in the western and eastern routes of the ITF and tracked both backward and forward in time. To assess the effects of flow variability that has a time scale longer than a day but shorter than a month, the definition of HFFV in this study, we conduct parallel experiments using daily and monthly averaged velocity fields. Particle trajectories reveal the contrasting circulation characteristics of the Sulawesi and Banda Seas. HFFV in the Sulawesi Sea (in the western route) is high, causing water to circulate longer over a broader area. The longer residence time in the Sulawesi Sea helps the upwelling of the inflowing Pacific waters, especially the intermediate water masses, to rise above 300 m at the Makassar Strait, and also has the potential to allow mixing processes to modify the water mass properties of the ITF. In contrast, HFFV is much lower in the Banda Sea and has minimal effects on the ITF.