Evidence of solar insolation and internal forcing of sea surface temperature changes in the eastern tropical Indian Ocean during the Holocene

The forcing and mechanisms governing sea surface temperature (SST) variations in the Indo-Pacific Warm Pool (IPWP) are complex. Insight into the full spectrum of IPWP climate dynamics, however, is limited by the spatial and temporal coverage of the climate data. In particular, the relationships among the changes in the SSTs, the precipitation patterns mainly associated with rainfalls from Asian Monsoons (AM), and the Indian Ocean Dipole (IOD) are poorly understood. To help us further assess the climate linkages, we have reconstructed a more spatial SST pattern during the Holocene by using multiple SST proxies (alkenone unsaturation index U37k' and Mg/Ca of planktic foraminifer) in the Eastern Tropical Indian Ocean (ETIO), the western margin of the IPWP based on three sedimentary cores from NW offshore of Sumatra, and offshore of Sumatra and Java (BS24, SO139-74KL, and SO184-100430). Stable hydrogen and carbon isotope records of terrestrial plant waxes from a nearby marine sediment core SO189-144KL and geochemical tracers measured from the coral reefs within the Mentawai Islands in the ETIO are used here as AM driven precipitation and IOD records in our data synthesis. Not surprisingly, our synthesis suggests that insolation plays a major role that has been responsible for the increased SSTs in ETIO since the early Holocene, while other mechanisms remain effective in determining the timing of our reconstructed SST variations. In particular, our SST pattern shares less similarity with that of coral Sr/Ca SST and is decoupled from the coral IOD events in the mid-Holocene. We interpret that our reconstructed ETIO SSTs are driven dominantly by the solar forcing, but are also affected by other internal climate mechanisms such as the local shifts in AM-controlled upwelling and precipitation, episodic reductions in the flow of warm western Pacific surface water into the Indian Ocean due to increased precipitation over the Indonesian archipelago, and long-term ENSO or IOD-like climate change.