AbstractThe effect of tides on the Indonesian Throughflow (ITF) is explored in a regional ocean model of South East Asia. Our model simulations, with and without tidal forcing, reveal that tides drive only a modest increase in the ITF volume, heat and salt transports toward the Indian Ocean. However, tides drive large regional changes in these transports through Lombok Strait, Ombai Strait and the Timor Sea, and regulate the partitioning of the ITF amongst them. The effect of tidal mixing on the salinity and temperature profiles within the Indonesian Seas drives a small decrease in the heat and salt transports toward the Indian Ocean in all three exit passages. In contrast, the tidal residual circulation due to the interaction between the tides and the topography and stratification (including the effects of tidal mixing on the circulation) leads to a large decrease in the transports toward the Indian Ocean through the Lombok and Ombai straits, but a large increase through the Timor Sea. Hence, the small net contribution from tides to the ITF's volume, heat and salt transports is due to a compensation between large, but opposing tidal residual transports at the combined Lombok and Ombai straits and in the Timor Sea. Our results indicate that explicit representation of tides, often missing in Earth system models, is necessary to accurately capture the ITF's pathway and so the tracer transport from the Pacific into the Indian Ocean.