HR: 17:30h
AN: PP14A-06    [Abstracts]
TI: A Holocene Record of Monsoon Intensity From Speleothems in Flores, Indonesia
AU: * Griffiths, M L
EM: Michael.Griffiths@newcastle.edu.au
AF: Environmental and Climate Change Research Group, The University of Newcastle, Callaghan, NSW 2308, Australia
AU: Drysdale, R
EM: Russell.Drysdale@newcastle.edu.au
AF: Environmental and Climate Change Research Group, The University of Newcastle, Callaghan, NSW 2308, Australia
AU: Gagan, M
EM: Michael.Gagan@anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
AU: Ayliffe, L
EM: linda.ayliffe@anu.edu.au
AF: Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
AU: Zhao, J
EM: j.zhao@uq.edu.au
AF: Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, QLD 4072, Australia
AU: St.Pierre, E
EM: e.stpierre@uq.edu.au
AF: Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, QLD 4072, Australia
AU: Hantoro, W
EM: hantoro@geotek.lipi.go.id
AF: Research and Development Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Bandung, 40135, Indonesia
AU: Suwargadi, B
EM: bambang.suwargadi@geotek.or.id
AF: Research and Development Center for Geotechnology, Indonesian Institute of Sciences (LIPI), Bandung, 40135, Indonesia
AB: The Australasian monsoon is among the largest monsoon systems on Earth. The affected region experiences a marked seasonal cycle in winds and precipitation, similar to its Northern Hemisphere counterparts (e.g., Asian monsoons). The Australasian monsoon is the life blood of the millions of people of the Indonesian archipelago. Since the climate is the dominating factor controlling food production, it is of great significance and urgency that we gain a firmer grasp on the parameters that control variations in monsoon intensity. Precise uranium series dating of two actively growing speleothems measuring ~1.25 (LR06-B1) and ~1.61 (LR06-B3) meters in length from Liang Luar cave (Flores, eastern Indonesia), reveal basal ages of ~12,846±103 and 23,605±171 years respectively. In previous studies, stable isotope ratios (δ¹⁸O and δ¹³C) and trace element concentrations in speleothems have revealed past environmental change (e.g., Burns et al., 2001; Wang et al., 2001; Fleitmann et al., 2004; Drysdale et al., 2004).In monsoon-affected regions, the δ¹⁸O signal recorded in stalagmites seems to be dominated by the amount of precipitation (so-called `amount effect'), whereby more negative (positive) δ<sup>18</sup>O values indicate enhanced (diminished) precipitation. Preliminary results from LR06-B1 indicate that δ<sup>18</sup>O values show a general increase in monsoon intensity from the beginning of the record to ~2000 years BP: this more or less follows insolation changes over the Australian continent.Comparison of our record with D4 from Dongge Cave reveals an anticorrelation during the Holocene, further supporting the hypothesis that tropical monsoon intensity is largely controlled by changes in insolation in both the Northern and Southern Hemisphere. Examination of our δ<sup>13</sup>C record demonstrates a high-frequency signal superimposed on low- frequency variability which correlates with the reconstructed sunspot cycle: higher (lower) sunspot numbers, and hence increased solar activity, correspond with higher (lower) δ<sup>13</sup>C values. An exception to this correlation is the abrupt shift towards higher δ<sup>13</sup>C values at approximately 1500 years BP, which does not correspond with the sunspot trend. This result may be indicative of a major volcanic eruption or the clearing of vegetation by modern humans; metal tools were introduced into the area just prior to this change. Given the lack of accurately dated palaeoclimate time series from the Australasian region, there is an urgent need for high-resolution records covering periods of known environmental change. Results from our study will contribute to a better understanding of tropical palaeoclimates and help scientists gain a clearer understanding of the mechanisms driving the changes in the Australasian monsoon system during the Holocene. Lastly, following the recent discovery of the `Hobbit' in a cave just a short distance from Liang Luar, there is scope for studying climatic conditions for the region around the time of the Hobbit's demise.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting