- Title
- Evidence for Holocene changes in Australian-Indonesian monsoon rainfall from stalagmite trace element and stable isotope ratios
- Creator
- Griffiths, Michael L.; Drysdale, Russell N.; Suwargadi, Bambang W.; Gagan, Michael K.; Frisia, Silvia; Zhao, Jian-Xin; Ayliffe, Linda K.; Hantoro, Wahyoe S.; Hellstrom, John C.; Fischer, Matthew J.; Feng, Yue-Xing
- Relation
- Earth and Planetary Science Letters Vol. 292, Issue 1-2, p. 27-38
- Publisher Link
- http://dx.doi.org/10.1016/j.epsl.2010.01.002
- Publisher
- Elsevier
- Resource Type
- journal article
- Date
- 2010
- Description
- Trace element and stable isotope ratios from an active stalagmite (LR06-B1) recovered from Liang Luar Cave on the island of Flores (eastern Indonesia) are used to reconstruct the position of the austral summer inter-tropical convergence zone and Australian-Indonesian summer monsoon variability during the Holocene. Uranium-series dating of the stalagmite shows that it commenced growth 12,640 years ago , with hiatuses spanning 8,560 to 6,420 and 3,670 to 2,780 years ago. Stalagmite Mg/Ca and Sr/Ca ratios correlate significantly with one another, and with δ¹⁸O and δ¹³C, throughout the record. This suggests that the Mg/Ca and Sr/Ca ratios are dominated by prior calcite precipitation, a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of Ca²⁺ ions (relative to Mg²⁺ and Sr²⁺) ‘upstream’ of the stalagmite. The degree of initial ²³⁴U/²³⁸U disequilibrium also appears to have been controlled by recharge to the overlying aquifer. Together with the Mg/Ca, Sr/Ca, and δ¹⁸O values, the initial uranium isotope activity ratios ([²³⁴U/²³⁸U]I) imply a generally drier early Holocene, coincident with a lower sea level and lower Southern Hemisphere summer insolation. Comparison of speleothem δ18O time-series from Flores and Borneo shows that they vary in unison for much of the Holocene. However, there is a significant decrease in the Borneo δ¹⁸O record ~6,000 to 4,000 years ago that does not occur in the Flores record. This anomaly may be related to a change in the Australian-Indonesian summer monsoon circulation in response to a protracted positive phase of the Indian Ocean Dipole. Under this scenario, stronger upwelling off of western Indonesia would, based on present-day effects, result in reduced summer convective activity over Flores and a subsequent northward shift of the intertropical convergence zone.
- Subject
- trace elements; speleothem; stable isotopes; Australian–Indonesian summer monsoon; inter-tropical convergence zone (ITCZ); Indian Ocean Dipole (IOD)
- Identifier
- http://hdl.handle.net/1959.13/923684
- Identifier
- uon:9790
- Identifier
- ISSN:0012-821X
- Language
- eng
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