Shallow throughflow variability in the outflow Straits of Indonesia



Since December 1995, the Indonesian throughflow has been monitored in five major passages as it flows from the Indonesian interior seas to the Indian Ocean. Pressure differences across the straits enable us to infer the geostrophic surface flow, and so provide the first simultaneous time-series measurements of surface geostrophic flow through these passages. Intraseasonal signals (30'90 day) are a ubiquitous feature in the surface flow, and are consistent with wind-forced Kelvin waves from both the eastern equatorial Indian Ocean and the south coast of Java. Using a relationship with surface velocity from three contemporaneous ADCP surveys, we approximate surface (0–100 m) volume transport fluctuations through four of the main exit passages. The amplitude of the total surface transport variation through these passages is fairly uniform, ranging from 10–15 Sv.