Destinations and Pathways of the Indonesian Throughflow Water in the Indian Ocean

Abstract

Abstract Passage of the Indonesian Throughflow (ITF) water through the Indian Ocean constitutes an essential section of the upper limb of the global ocean conveyor belt. Although existing studies have identified a major exit of the ITF water to the Atlantic Ocean through the Agulhas Current system, our knowledge regarding other possible destinations and primary pathways remains limited. This study applies the Connectivity Modeling System (CMS) particle tracking algorithm to seven model-based ocean current datasets. The results reveal a robust return path of the ITF water to the Pacific Ocean. The partition ratio between the Atlantic and Pacific routes is 1.60 ± 0.54 to 1, with the uncertainty representing interdataset spread. The average transit time across the Indian Ocean is 10–20 years to the Atlantic and 15–30 years to the Pacific. The “transit velocity” is devised to describe the three-dimensional pathways in a quantitative sense. Its distribution demonstrates that the recirculation structures in the southwestern subtropical Indian Ocean favor the exit to the Atlantic, while the Antarctic Circumpolar Current in the Southern Ocean serves as the primary corridor to the Pacific. Our analysis also suggests the vital impact of vertical motions. In idealized tracing experiments inhibiting vertical currents and turbulent mixing, more water tends to linger over the Indian Ocean or return to the Pacific. Turbulence mixing also contributes to vertical motions but only slightly affects the destinations and pathways of ITF water.