Abstract
The strontium isotopic compositions (87Sr/86Sr) of samples including soils, bedrock, soil waters, drip waters and their corresponding speleothems in the Qixing Cave (QXC), Guizhou Province, China, were systemically measured and analyzed. The results indicate that there are significant Sr isotopic differences among samples. The mean 87Sr/86Sr ratios in drip water for the samples 1#, 4# and 9# were 0.709568, 0.709139 and 0.708761, respectively, which possibly result from different flow paths, residence times, and other hydrogeological processes in the unsaturated zone overlying QXC. Meanwhile, levels of 40.8%, 57.6% and 72.4% of Sr in drip waters for 1#, 4# and 9#, respectively, were derived from bedrock dissolution, which was calculated by the mixture model of the two end-members (soil and bedrock). There is, however, no positive correlation between the relative proportion from bedrock dissolution (δ 13C value is 1.8‰) and drip water δ 13CDIC values. The mean drip water δ 13CDIC value in 1# is the heaviest (−4.5‰) with the lowest contribution rate of bedrock dissolution, whereas the value in 9# is the lightest (−9.3‰) with the highest contribution rate of bedrock dissolution. The proportion from host rock dissolution in 4# is higher than that in 1# and lower than that in 9#, while its mean drip water δ 13CDIC value (−8.6‰) is higher than that of 9# and lower than that for 1#. This suggests that the prior calcite precipitation (PCP) processes in the unsaturated zone overlying the cave are responsible for the δ13CDIC value differences between different drip waters, and not bedrock dissolution. Furthermore, this study also demonstrates that the 87Sr/86Sr ratios of speleothems in the 1# and 4# mainly reflect the variation in the relative proportions from the soil system (soil water) and bedrock dissolution overlying the cave. It is, therefore, feasible to use the strontium isotopic signals of speleothems as an indicator for soil chemical weathering intensity, and consequently as a monsoon proxy in the study area.
Highlights
The strontium isotopic compositions (87Sr/86Sr) of samples including soils, bedrock, soil waters, drip waters and their corresponding speleothems in the Qixing Cave (QXC), Guizhou Province, China, were systemically measured and analyzed
Many significant achievements have been made on 87Sr/86Sr ratio in speleothems, there are few studies about the Sr isotopic compositions of different components in cave system
It is difficult to distinguish the relative proportions of Sr from various Sr sources composed of different Sr isotopes, and results can lead to various interpretations as a climate and environment proxy [2,5,6]
Summary
The strontium isotopic compositions (87Sr/86Sr) of samples including soils, bedrock, soil waters, drip waters and their corresponding speleothems in the Qixing Cave (QXC), Guizhou Province, China, were systemically measured and analyzed. This study demonstrates that the 87Sr/86Sr ratios of speleothems in the 1# and 4# mainly reflect the variation in the relative proportions from the soil system (soil water) and bedrock dissolution overlying the cave It is, feasible to use the strontium isotopic signals of speleothems as an indicator for soil chemical weathering intensity, and as a monsoon proxy in the study area. Our previous work has shown that it is difficult to distinguish the relative effects of host rock dissolution and prior calcite precipitation (PCP) processes based on C isotopic variabilities in drip water in the QXC [7] because both of them could result in the drip water δ13CDIC signal becoming heavier. This allowed us to further investigate the effects of hydrogeochemical processes on the C isotopic signals in drip water, which would provide a fundamental theoretical support for reconstructing paleoclimate from speleothem Sr isotopes
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