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

Vinu Valsala,Shamil Maksyutov

doi:10.1155/2010/540783

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.

Highlights

The Indonesian Throughflow (ITF) is a system of currents flowing from the Pacific to the Indian Ocean via the Indonesian Straits
In order to verify the pathways resolved in our Ocean General Circulation Model (OGCM), we examined the ocean reanalysis data set derived from Simple Ocean Data Assimilation (SODA 2.0.2) prepared by Carton and Giese [32]
An important question emerges out is, whether all the particles that upwell in the south Java coast follow the same pathway, or do they spread over the surface ocean and are carried westward? In order to illustrate a complete trajectory of all the ITF watermass that upwell in the Java coast, we further examined the pathways of Tracer-3

Summary

Introduction

The Indonesian Throughflow (ITF) is a system of currents flowing from the Pacific to the Indian Ocean via the Indonesian Straits. Valsala and Ikeda [10] found that the ITF, from its exit region to the western tropical Indian Ocean, has two major pathways: (1) a surface branch that advects along the Leeuwin current system and subducts offnorthwestern coast of Australia and flows northwestward along the thermocline depth, and (2) a subsurface branch. Upwelling in the south Java coast may bring both the Indian Ocean water of the exit region as well as the ITF water to the surface. Separating these two components becomes difficult from the limited observations of temperature, salinity or any other biogeochemical tracer.

OGCM and Methods

Upwelling of ITF in South Java Coast

Tracer Experiments Using Reanalysis Ocean Data

Volume Transport in the Upwelling Pathways

Findings

Discussion and Conclusion