NOAA/WDS Paleoclimatology - Eastern Indian Ocean Biomarker Data and Sea Surface Temperature Reconstructions from 3.5 - 1.5 Ma

Ocean gateways facilitate circulation between ocean basins, thereby impacting global climate. The Indonesian Gateway transports water from the Pacific to the Indian Ocean via the Indonesian Throughflow (ITF) and drives the strength and intensity of the modern Leeuwin Current, which carries warm equatorial waters along the western coast of Australia to higher latitudes. Therefore, ITF dynamics are a vital component of global thermohaline circulation. Plio-Pleistocene changes in ITF behavior and Leeuwin Current intensity remain poorly constrained due to a lack of sedimentary records from regions under its influence. Here, organic geochemical proxies are used to reconstruct sea surface temperatures (SST) on the Northwest Australian shelf at IODP Site U1463, downstream of the ITF outlet and under the influence of the Leeuwin Current. Our new records, based on TEX86 and the long-chain diol index (LDI), provide insight into past ITF variability (3.5 to 1.5 Ma) and confirm that SST exerted a control on Australian continental hydroclimate. A significant TEX86 cooling of ca. 5°C occurs within the mid-Pliocene Warm Period (mPWP; 3.3 to 3.1 Ma) suggesting this interval was characterized by SST fluctuations at Site U1463. A major feature of both the TEX86 and LDI records is a strong cooling from ~1.7 to 1.5 Ma. We suggest this event reflects a reduction in Leeuwin Current intensity due to a major step in ongoing ITF constriction, accompanied by a switch from South to North Pacific source waters entering the ITF inlet. Our new data suggest that an additional ITF constriction event may have occurred in the Pleistocene.