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Title: Rainfall variability and temporal changes in the dead carbon fraction in an Indonesian speleothem
Authors: Hua, Q
Griffiths, ML
Drysdale, R
Bajo, P
Jenkins, D
Hellstrom, JC
Johnson, KR
Gagan, MK
Zhao, JX
Keywords: Monsoons
Isotope dating
Issue Date: 1-Jan-2016
Publisher: Australasian Quaternary Association Inc.
Citation: Hua, Q., Griffiths, M., Drysdale, R., Bajo, P., Jenkins, D., Hellstrom, J., Johnson, K., Gagan, M., & Zhao, J. (2016). Rainfall variability and temporal changes in the dead carbon fraction in an Indonesian speleothem. Papers presented at the AQUA Biennial Conference, "Quaternary Perspectives from the City of Volcanoes" Old Government House, University of Auckland, New Zealand, 5-9 December 2016. Abstracts retrieved from,-46,6.
Abstract: The number of speleothem-based paleoclimate records has increased significantly in recent years. To assess the potential hydrological control on speleothem radiocarbon variability, we constructed a high-resolution dead carbon fraction (DCF) record from a speleothem from Flores, Indonesia for two different periods, the Younger Dryas (YD) chronozone and the Last Millennium. A total of thirty-four 14C analyses were conducted on calcite extracted from U-Th dated stalagmite LR06-B1. To better characterise the paleoclimate and environmental changes, highresolution stable-isotope (δ18O, δ13C) and trace-element (Mg/Ca, Sr/Ca) measurements were also conducted along the same stalagmite sections. Broad comparison of the DCF record with the hydrologically-controlled proxy data suggests that rainfall increases were matched by DCF increases. In line with a previous interpretation of DCF variability for the same specimen, but during the interval 2.4-2.8 ka and the post-bomb period, we interpret the DCF during the YD and the Last Millennium to have been primarily controlled by limestone dissolution associated with changes in open- versus closed-system conditions, rather than other potential factors such as kinetic fractionation and/or variations in the age-spectrum of soil organic matter above the cave. It then follows that more abundant monsoon rainfall in Flores resulted in the soil-karst system being in a more closed state, which inhibited carbon isotope exchange between the karst-water dissolved inorganic carbon and soil-gas CO2, and ultimately led to a greater contribution of dead-carbon from the bedrock. Our results indicate that DCF in tropical speleothems can be used as a proxy of past rainfall and consequently monsoon variability.
Gov't Doc #: 7727
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