Role of the Indian Ocean Wind-Driven Dynamics in the Indonesian Throughflow Variability

Abstract

The Indonesian Throughflow (ITF) regulates heat and freshwater distributions over the Indo-Pacific Oceans and fundamentally affects the climate. The past decade has witnessed acute interannual variations in the volume transport within the Makassar Strait—the main ITF inflow passage—such as a decrease of ∼4 Sv (1 Sv ≡ 10⁶ m³ s⁻¹) in 2015–2016 boreal winter and an enhancement of ∼3 Sv in 2017 autumn, relative to a mean transport of ∼12 Sv. The Pacific Ocean dynamics, dictated largely by El Niño-Southern Oscillation (ENSO), cannot fully explain these variations, and a quantitative understanding of the Indian Ocean (IO) dynamics involved in the ITF transport variability remains lacking. Here, by performing regional forcing experiments with a 0.1° ocean general circulation model, we reveal that the wind-driven IO dynamics have operated as a buffering effect for ∼56% of the time and a reinforcing effect for ∼44% of the time during the past decade. Notably, the IO dynamics buffered the weakened ITF by ∼2 Sv in 2015–2016 winter and contributed to the enhanced ITF by ∼0.5 Sv in 2017 autumn. The buffering effect of IO winds is commonly seen during strong ENSO events, while the reinforcing effect arises from Indian Ocean Dipole (IOD) events independent of ENSO. Our study aids in the prediction of the ITF strength under the amplifying ENSO and IOD variabilities expected in a warming climate.