Compound-specific carbon isotope records of vegetation and hydrologic change in central Sulawesi, Indonesia, since 53,000 yr BP
Lake Matano (2°29.1′S 121°20′E) in central Sulawesi, the deepest and one of the largest lakes in Indonesia, provides an excellent opportunity to reconstruct long-term hydrological and vegetation changes at the heart of the Maritime Continent within the tropical Western Pacific Warm Pool. We measured the carbon isotopic composition of terrestrial leaf waxes (δ13Cwax) in new sediment cores from Lake Matano to understand regional variations in vegetation and their interactions with local and high latitude climate forcings during the past 53 kyr. Variations in δ13Cwax record the expansion and contraction of C3 versus C4 vegetation as well as changes in plants' carbon and water use efficiency and, by inference, regional hydroclimate. During Marine Isotope Stages 1 and 3, more negative δ13Cwax values indicate that closed-canopy C3 rainforests predominated in Sulawesi, reflecting a wetter, less seasonal climate. In contrast, more positive δ13Cwax values record a terrestrial ecosystem with more abundant open canopy vegetation and possible expansion of C4 grasses between 29 and 14 ka BP, indicating that during Marine Isotope Stage 2, including the Last Glacial Maximum, the climate was more arid, likely with increased precipitation seasonality, in central Sulawesi. Comparison of our record with other paleovegetation and paleohydrological records from Sulawesi and nearby islands suggests coherent long-term hydrological changes in central Indonesia that appear to be sensitive to high latitude climate across glacial-interglacial boundaries. However, variations in the amplitude of the response of vegetation to these glacial-interglacial forcings highlight the importance of regional topographic control on climate and vegetation and suggest an important role for higher elevations in maintaining rainforest refugia during regionally arid time intervals when C4 savannas and grasslands expanded at lower elevations.