A Short Surface Pathway of the Subsurface Indonesian Throughflow Water from the Java Coast Associated with Upwelling, Ekman Transport, and Subduction

Abstract

A surface pathway of the subsurface Indonesian Throughflow (ITF) in the southeastern Indian Ocean is proposed using a combined analysis of Lagrangian particles and passive tracers derived from two independent tools: an Ocean General Circulation Model (OGCM) and Simple Ocean Data Assimilation (SODA.2.0.2) reanalysis data. This newly suggested pathway follows the processes in succession as upwelling in the south Java coast, offshore Ekman drift and subduction into the thermocline centered on 20 ∘ S. The upwelling of subsurface ITF along the south Java coast is found to occur from August to October. Upon surfacing, the ITF advects southwestward being trapped in the surface Ekman layer for an approximate period of 260 days and reaches the southeastern tropical Indian Ocean subduction zone centered on 20 ∘ S which is demarcated by the Zero Wind Stress Curl (ZWSC) and subducts there. The particle trajectory revealed that during the subduction within the ZWSC region, the surface eastward flow above 120 m depth carries the particle about 10 ∘ to the east and westward flow below this depth carries the particle to the western Indian Ocean along the thermocline. These pathways are confirmed by a series of tracer experiments using SODA reanalysis data. The effects of vertical mixing and entrainment on the surfacing of the ITF at south Java coast were identified.