Hydroclimate changes in the Maritime Continent over the past 30,000 years recorded by speleothems from Sulawesi, Indonesia

• Main Author: Yuan, Shufang
• Other Authors: Wang Xianfeng
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2019
• Subjects: DRNTU::Science::Physics::Meteorology and climatology
• Online Access: https://hdl.handle.net/10356/105866; http://hdl.handle.net/10220/47874
• Institution: Nanyang Technological University

I use calcite speleothems from southwestern Sulawesi, Indonesia, to reconstruct changes in the regional hydroclimate and vegetation during the past 30,000 years. The reconstructions are based on multi-proxy records comprised of oxygen (δ18O) and carbon (δ13C) isotopic data and trace element ratios dated by high-precision uranium-thorium disequilibrium dating methods. The δ18O record shows increased strength of moisture convection in the Maritime Continent from the last glacial period to the Holocene. The δ13C and Mg/Ca records suggest a forest expansion coupled with increased soil CO2 production. These glacial-interglacial changes in the regional hydroclimate and vegetation correspond to the rising of sea surface temperature and atmospheric CO2 concentration, and Sunda Shelf flooding. Comparisons between the Sulawesi δ18O and other speleothem δ18O records from the Maritime Continent suggest that the southern extent of the regional mean ITCZ has likely been between southwestern Sulawesi and Flores, which are fewer than 300 km apart, during the past 30,000 years. Based on the Sulawesi and Flores records, I have then derived an ITCZ index, which allows the characterization of the relative movements of the ITCZ. The index indicates that ITCZ migration is driven by precession on the orbital timescale, coupled with changes in climate boundary conditions and ocean circulations. Further synthesis of tropical and subtropical speleothem δ18O shows that, similarly to what can be observed today in rainfall δ18O, the continental rainout effect has primarily controlled the spatial distribution of speleothem δ18O during the past 30,000 years, with isotopic fractionation having been dominated by temperature and continental water recycling. On the glacial-interglacial timescale, speleothem δ18O has largely followed nearby sea surface temperature at upstream monsoonal and maritime sites, but at downstream monsoonal sites and sites located south of the ITCZ, it instead followed precessional insolation. Temporally, tropical-subtropical speleothem δ18O variation has been predominately influenced by ITCZ migration since the LGM, with secondary influences from deep tropical convection during the Holocene.