Monitoring the Indonesian Throughflow in Makassar Strait

DESCRIPTION: Moorings deployed earlier in the Makassar Strait will be maintained to continue to measure throughflow, temperature, velocity, and salinity.

OUTCOMES: The Makassar Strait throughflow of ~12 - 13 Sv, representing ~77% of the total Indonesian Throughflow, displays fluctuations over a broad range of time scales, from intraseasonal, to seasonal (monsoonal) and interannual scales. We now have 13.3 years of Makassar throughflow observations: November 1996 - early July 1998; January 2004 - August 2011; August 2013 - August 2017. Strong southward transport is evident during boreal summer, modulated by an ENSO interannual signal, with weaker southward flow and a deeper subsurface velocity maximum (V-max) during El Niño; stronger southward flow with a shallower V-max during La Niña. Accordingly, the southward heat flux, a product of the along-channel current and temperature profiles, is significantly larger in summer and slightly larger during La Niña. The southward flow relaxed in 2014 and more so in 2015/16, similar though not as extreme as during the strong El Niño event of 1997. In 2017 the throughflow increased to ~20 Sv. Since 2016 the deep layer, 300-760 m southward transport increases, almost doubling to ~7.5 Sv. From mid 2016 into early 2017 the transport above 300 m and below 300 m are about equal, whereas previously the ratio was about 2.7:1. Near zero or northward flow occurs in the upper 100 m during boreal winter, albeit with interannual variability. Particularly strong winter reversals were observed in 2014/15 and 2016/17, the latter being the strongest winter reversal revealed in the entire Makassar time series.