Hydrological connectivity and mixing of Lake Towuti, Indonesia in response to paleoclimatic changes over the last 60,000 years

Abstract

The Indo-Pacific Warm Pool (IPWP) is an important driver of global climate, but its response to and involvement in paleoclimate change is poorly constrained. We generated a new record of sediment geochemistry from Lake Towuti (2.5°S, 121.5°E), Indonesia, located in the heart of the IPWP, to investigate changes in hydrological connectivity with upstream lakes and the extent of lake mixing and oxygenation during paleoclimate changes over the last 60,000years BP (60ka). Lake Towuti is located at the downstream end of the Malili Lakes, a chain of large, ancient, and biologically diverse tectonic lakes occupying a geologically heterogeneous terrain in central Sulawesi, Indonesia. Major and trace element data from river and lake sediments suggest no changes in sediment provenance during the Last Glacial Maximum (LGM), indicating that some of the Malili Lakes remained hydrologically open despite a regionally drier climate. However, samples from the LGM are uniformly less enriched in trace elements than samples from the Holocene and Marine Isotope Stage 3 (MIS3), which suggests a decrease in weathering intensity during the LGM, likely in response to decreased precipitation and temperature. Changes in Fe and other redox-sensitive trace element concentrations indicate changes in water column oxygenation, with the highest oxygen availability occurring during the LGM (15–35ka) likely due to more frequent and/or deeper mixing of Lake Towuti's water column. The glacial–interglacial trend in lake oxygenation corresponds with changes in regional precipitation and associated changes in the seasonal cycle. The high degree of faunal endemism in these lakes may be related to changes in the lake geochemistry associated with glacial–interglacial environmental variability driven by changing inputs and redox variability.