The advection of relatively fresh Java Sea water through the Sunda Strait is presently responsible for the low-salinity tongue in the eastern tropical Indian Ocean with salinities as low as 32. The evolution of the hydrologic conditions in the eastern tropical Indian Ocean since the last glacial period, when the Sunda shelf was exposed and any advection via the Sunda Strait was cutoff, and the degree to which these conditions were affected by the Sunda Strait opening are not known. Here we have analyzed two sediment cores (GeoB 10042-1 and GeoB 10043-3) collected from the eastern tropical Indian Ocean off the Sunda Strait that cover the past similar to 40,000years. We investigate the magnitude of terrigenous supply, sea surface temperature (SST), and seawater O-18 (O-18(sw)) changes related to the sea level-driven opening of the Sunda Strait. Our new spliced records off the Sunda Strait show that during the last glacial, average SST was cooler and O-18(sw) was higher than elsewhere in the eastern tropical Indian Ocean. Seawater O-18 decreased similar to 0.5 after the opening of the Sunda Strait at similar to 10kyr B.P. accompanied by an SST increase of 1.7 degrees C. We suggest that fresher sea surface conditions have persisted ever since due to a continuous transport of low-salinity Java Sea water into the eastern tropical Indian Ocean via the Sunda Strait that additionally increased marine productivity through the concomitant increase in terrigenous supply.