Unprecedented Response of Indonesian Throughflow to Anomalous Indo-Pacific Climatic Forcing in 2016

The Indonesian Throughflow (ITF) transport in the upper layer of Makassar Strait was reduced by an unprecedented 25-40% during June to September 2016, the weakest northern summer ITF transport measured through 2004 to mid-2017. A negative Indian Ocean Dipole (IOD) event occurring through boreal summer and fall 2016 was the main driver for the reduced ITF transport. Elevated sea surface temperature and height off the southern coast of Sumatra and Java islands, attributed to the IOD event, suppressed the Pacific to Indian pressure gradient, resulting in a reduction in the ITF transport. Intensified Wyrtki jets, energetic westerly winds, and downwelling Kelvin waves associated with the strong IOD event contributed to the suppressed interocean pressure gradient. The influence from the 2016 La Nina event on the other hand was secondary. This study showcases the role of coupled ocean-atmosphere interactions in Indian Ocean in regulating an extreme interannual variation of the ITF in 2016, which is a unique event in the observational record.