http://nova.newcastle.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9792 We have applied a new technique to analyze the oxygen (δ¹⁸O) and hydrogen (δD) isotope ratios in speleothem fluid inclusions to reconstruct the temperature and rainfall history of southern Indonesia during the Younger Dryas (YD) event and the Holocene. The 12,640-year speleothem record, anchored by 33 uranium-series dates, shows that fluid-inclusion δ¹⁸O values vary in phase with speleothem calcite δ¹⁸O during the Holocene, suggesting that the speleothem calcite δ¹⁸O primarily reflects variations in the δ¹⁸O of local rainfall. Significant early to mid-Holocene decreases in both δ¹⁸O series are interpreted as an intensification of Australian–Indonesian summer monsoon rainfall in response to deglacial eustatic sea-level rise and flooding of the Sunda Shelf. Cave drip-water temperatures reconstructed from coupled measurements of δ¹⁸O in speleothem calcite and fluid inclusions remained relatively constant through the Holocene. This is consistent with reconstructions of Indo-Pacific sea-surface temperature (SST) based on analysis of Mg/Ca ratios in planktonic foraminifera. However, during the YD event, drip-water (i.e. cave) temperature was ~ 5 °C cooler than modern, which is substantially cooler than SSTs inferred from foraminiferal Mg/Ca, but consistent with coral Sr/Ca reconstructions of SST and terrestrial evidence for high-elevation snow-line depressions. Lower fluid-inclusion δ¹⁸O values during the YD indicate that the cooling was accompanied by increased monsoon rainfall. Taken together, the results suggest that the southerly penetration of the intertropical convergence zone (ITCZ) was largely influenced by the cross-equatorial temperature gradient, rather than local SSTs (and air temperatures). Our results provide new evidence for a rapid cooling of deep tropical air temperatures and repositioning of the ITCZ during the YD event. 2012-01-12T05:50:04.922Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:9790 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. 2012-01-12T05:30:04.114Z ]]> http://nova.newcastle.edu.au/vital/access/manager/Repository/uon:5064 Speleothems are regarded as major palaeoclimate and palaeoenvironmental archives, notably because of their records of oxygen and carbon isotopic variations, which arc constrained in a reliable chronological framework with U-series dating. Increasingly studied, these isotopic signals are, however, complex and their interpretation must be based on a good knowledge of the isotopic fractionation conditions during calcite precipitation and of the context of speleothem formation. This paper presents a bibliographic review of the use of speleothem stable isotopes in palaeoclimate and palaeoenvironmental reconstruction. The physico-chemical processes that combine to determine the isotopic composition of the precipitated calcite arc first presented. Then, the limits and uncertainties associated with the interpretation of these isotopic signals are discussed, along with the means by which to identify isotope signal disturbances. 2010-04-27T04:35:10.775Z ]]>