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Cave monitoring is crucial for the interpretation of climatic and environmental significances of various geological proxies in speleothem. Therefore, the hydrochemical and stable isotopic compositions (δ18O, δD, Mg/Ca, Sr/Ca, and Ba/Ca) of karst cave waters during 2005–2016 A.D. were constantly monitored in Furong Cave, Chongqing City, Southwest China. A comparison with local hydrothermal conditions led to a few conclusions as follows: (1) The Mg/Ca ratio is significantly responsive to the changes in drought/wet conditions outside the cave, which increased in drought years and decreased in wet years, respectively. Seasonal variation of Sr/Ca is more significant than those of Mg/Ca and Ba/Ca ratios. (2) Prior calcite precipitation (PCP), incongruent calcite dissolution (ICD), water-rock interaction (WRI), and pCO2 of soil and cave air, may account for the changes in trace element ratios in the epikarst, which resulted in a complex variation of element ratios in the cave drip water. In general, WRI in drought years is stronger than that in wet years, and that in low discharge sites is stronger than in high discharge sites. Seasonal variation of Ca2+ concentration, induced by PCP, exerts significant impact on the evolution of Sr/Ca ratio in drip water. (3) δ18O and δD of drip water are influenced by the "mixing effect", leading to the result that their seasonal variations are less significant than that of precipitation. (4) At least in the study period, the ratios of trace elements in the drip water in Furong Cave mainly reflected the variations of local hydrological conditions (drought or wet) dominated by precipitation. In contrast, changes in δ18O and δD did not exhibit the "amount effect" in drip water on monthly timescale. High-resolution δ18O record (e.g., seasonal and annual) of speleothem in Furong Cave may not be recommendable. However, the δ18O is potentially a reliable proxy in speleothems to record the change of rainfall on interannual and longer timescales. Furthermore, on interannual timescale, large scale variation of atmospheric circulation, such as El Niño-Southern Oscillation (ENSO), can change the δ18O of precipitation and that of drip waters by changing the moisture source at different atmospheric circulation conditions. [ABSTRACT FROM AUTHOR]

Abstract: To facilitate the measurement of U–Th isotopic compositions suitable for high-precision and high-resolution 230Th dating of coral and speleothem carbonates, secondary electron multiplier (SEM) protocol techniques for multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) have been developed. The instrumental sensitivities are 1–2%, with a precision of ±1–2‰ (2σ) for abundance determination of 50–200fg 234U (1–4ng 238U) or 230Th. This method features chemistry refinements, improvements to procedural and instrumental blanks, spectral inference reductions, and careful consideration of non-linear SEM behavior. Measurement consistency of this MC-ICP-MS combined with previous mass spectrometric results on U–Th standards and a variety of carbonates demonstrates the validity of the SEM protocol method. For fossil corals, a routine U–Th isotopic determination at permil-level precision requires only 10–50mg of carbonate. As little as 200mg of young coral with an age of less than 20yr can be dated with a precision of ±0.3–0.8yr. About 20–200mg speleothem samples with sub-ppm-to-ppm U are required to earn a 5‰ precision on ages from 5 to 100kyr. Requirement of small sample size, 10–100s mg carbonate, can permit high temporal resolution to date speleothems with slow growth rates, i.e., 1–10mm/kyr. This high-precision 230Th chronology is critical to accurately establish age models, date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography. The U–Th isotopic determination techniques described here can also be applied to different environmental samples, such as waters, rocks, and sediments. [Copyright &y& Elsevier]

Abstract: A 7-cm long aragonite stalagmite, FR0510-1, from Furong Cave, Chongqing, was dated by 210Pb and 230Th methods, revealing a-2000-year record of climate history under the influence of the East Asian Monsoon. The FR0510-1 record resembles Dongge Cave DA record on 10–100-year scales, but quite different from the Wanxiang Cave WX42B record, indicating that while stalagmite δ18O record represents local/regional moisture change, spatial variability of the monsoonal rainfall over eastern China must take into account. During the past 2000years, climate in Chongqing was relatively wet in the intervals of 50 BC–AD 250, AD 1150–1450 and AD 1600–1950, and relatively dry during the periods of AD 250–1150 and AD 1450–1600. Dry conditions were prevailing over the Medieval Warm Period, whereas wet climates were dominant during the most time of the Little Ice Age in Chongqing area. [Copyright &y& Elsevier]