Role of the Indian Ocean dynamics in the Indonesian Throughflow variability and extremes

Abstract

The Indonesian throughflow (ITF) regulates heat and freshwater distributions of the Indo-Pacific Oceans and fundamentally affects the climate. The past decade has witnessed acute interannual variations in the Makassar Strait – the main ITF inflow passage, reaching monthly extremes of 1.9 Sv (1 Sv ≡ 10⁶ m³ s^-1) in 2015 and 16.6 Sv in 2017, compared with a mean transport of ~12 Sv. The Pacific Ocean dynamics dictated by El Niño/Southern Oscillation (ENSO) cannot fully explain these variations and the role of the Indian Ocean (IO) dynamics remains uncertain. Here, we use a 0.1°, quasi-global ocean model to cleanly isolate the impact of the IO dynamics on the ITF. The wind-driven IO dynamics are found to play a significant role in either buffering or driving ITF variability. The buffering effect is commonly seen during strong ENSO events, while the driving effect arises from Indian Ocean dipole (IOD) events independent of ENSO. Notably, the IO dynamics buffered the weak ITF extreme of 2015 by ~35% and contributed to the strong ITF extreme of 2017 by ~23%. Our study aids in the prediction of regional climate extremes under the intensifying ENSO and IOD scenarios expected in the future.