The consequences of opening the Sunda Strait on the hydrography of the eastern tropical Indian Ocean

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 ~40,000 years. We investigate the magnitude of terrigenous supply, sea surface temperature (SST), and seawater δ18O (δ18Osw) 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 δ18Osw was higher than elsewhere in the eastern tropical Indian Ocean. Seawater δ18O decreased ~0.5‰ after the opening of the Sunda Strait at ~10 kyr B.P. accompanied by an SST increase of 1.7°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. Key Points Reconstruction of surface conditions off the Sunda Strait over the past 40 kyr Fresher surface condition during the Holocene compared to last glacial Java Sea waters have contributed to hydrology change off the Sunda Strait