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Studies have shown that stable isotope [oxygen (O) and carbon (C)] composition of mammal tooth enamel can provide information on a region's paleoclimate and paleoecology. Stable isotope analysis has been used to investigate the impact of the Qinghai–Tibetan Plateau uplift on the development and strength of the Asian monsoon. However, due to sparse data from southern China, a region dominated by the East Asian monsoon, O and C isotope analysis of mammal tooth enamel has been unable to fully inform on the impact of the monsoon environment in the region. Here, we present the results of the analysis of stable isotopes on a set of cervid tooth enamel from late Middle Pleistocene Tantang Cave in Bubing Basin, Guangxi, southern China and compare them with comparable isotope data from nearby early Early Pleistocene Mohui and middle Early Pleistocene Sanhe Caves. The results of the oxygen isotope analysis indicates that Tantang Cave (−8.70‰ to −6.39‰) is similar to Mohui Cave (−8.71‰ to −6.34‰), with both sites being more negative than Sanhe Cave (−4.77‰ to −1.20‰). We suggest the East Asian summer monsoon was stronger during the Tantang and Mohui mammal occupations and weaker during the lifetime of the Sanhe mammals. This result is indirectly corroborated by vertebrate paleontological evidence. Murid rodents, implying an open grassland and somewhat drier climate, are found in great numbers in Sanhe. The carbon isotope results from Tantang (−17.70‰ to −10.26‰), Mohui (−15.27‰ to −12.51‰), and Sanhe (−16.63‰ to −14.71‰) overlap extensively suggesting these various faunas primarily lived in a closed forest environment. The implications of these findings from stable isotope studies from Tantang are discussed in their broader context. [ABSTRACT FROM AUTHOR]

The timing and structure of the past weakening monsoon events, such as the 2.8 ka BP event, is critical for testing the simulation experiment of extreme climate prediction in the future. But the lack of continuous records with high resolution based on precise chronology during 2.8 ka BP hinders the better understanding of the event. In this study, we present a new annually-resolved stalagmite δ18O record covering the 2.8 ka BP event with precisely independent chronology from Central China. Combined with other 7 well-dated stalagmite δ18O records from East China covering 2.8 ka BP period with resolution less than 10 years, the Asian summer monsoon (ASM) signal has been extracted by the principal component analysis (PCA), and the ASM sequence has been built by the first principal component (PC1) on a decadal scale. Two weakening anomalies of the ASM are presented by PC1 during the 2.8 ka BP event and this event has been identified by 1 standard deviation with an asymmetric two-plunging structure and a duration of ∼310 years. The comparisons between the ASM weakening derived from multiple stalagmite δ18O records in this study and the solar insolation minimum with the North Atlantic cooling, suggest that the synchronous North Atlantic cooling should play an important role on the monsoon weakening in East Asia, while the delayed insolation minimum must be impossible to trigger the 2.8 ka BP event. But low solar radiation may magnify the variation amplitude of the monsoon weakening around 2.7 ka BP, which suggest both internal variability and external forcing impact on the 2.8 ka BP event. • Demonstrate a unique annual laminated speleothem δ18O record around the 2.8 ka event from Central China. • Extract two weakening monsoon anomalies in East China during the 2.8 ka BP by PC analysis on multiple stalagmite δ18O records. • Precisely identify the whole duration of the 2.8 ka BP event by ∼310-year with a two-plunging structure. • It is the North Atlantic cooling, rather than the solar insolation, that triggered the 2.8 ka BP event. [ABSTRACT FROM AUTHOR]

Abstract: Despite considerable work on other trace elements, the incorporation of dissolved silicon from cave waters into speleothems has not been previously investigated. In this study, the controls on dissolved Si in cave waters and on adsorbed Si in resulting speleothems are therefore investigated. Bedrock (dolomite), soil water, dripping water, and cave carbonates were retrieved from Heshang Cave situated in the central Yangtze valley of China and were subjected to analysis of dissolved Si content (plus accompanying Ca and Fe analyses). Soil waters have Si/Ca of 45.5 mmol/mol, compared to only 3.2 mmol/mol in the dolomite bedrock, demonstrating that >80% of the dissolved Si must come from dissolution of silicate minerals in the soil. Drip waters have a dissolved Si concentration of ¿4.2 µg/mL, similar to that in the overlying soil water. Actively growing cave carbonates have a Si/Ca of 0.075 mmol/mol suggesting a partition coefficient for incorporation of dissolved silicon of 0.0014, in good agreement with previous laboratory studies. Extrapolating the results of these laboratory studies to the cave environment suggests that changes in Si/Ca in cave carbonates are likely to be primarily controlled by changes in drip-water Si/Ca. The drip-water Si/Ca will, in turn, be controlled by the rate of wind-blown silicate supply; by soil weathering rates; by rainfall dilution; and by precipitation of calcite. The general expectation is that these effects combine to produce high Si/Ca in speleothems during times of low rainfall. A d18O record from a Heshang Cave stalagmite which grew between 20 and 11 thousand years ago allows these controls to be tested. Correlation of high Si/Ca with high d18O demonstrates that regional rainfall exerts significant (but not complete) control on speleothem Si/Ca. With further understanding, speleothem Si/Ca may provide a proxy for past rainfall to complement existing proxies such as d18O and Mg/Ca. [Copyright &y& Elsevier]

There is a great need for the reconstruction of independent El Niño Southern Oscillation (ENSO) from different archives and locations to provide a robust understanding of its driving and feedback mechanisms on long time scales. Though tree-ring cellulose δ18O (δ18O TR) records from the East Asian monsoon (EAM) region of China have the potential to reconstruct ENSO on an annual time scale, δ18O TR ENSO signals may be masked by local climate effects since any individual δ18O TR record is influenced by both large-scale atmospheric circulation and local climate. Few attempts have been made to reduce the uncertainties of the reconstructed ENSO index by δ18O TR records from the EAM region of China by ensemble data analysis. In this study, twelve published δ18O TR records spanning over 100 years (1902–2003 CE) have been collected and processed using principal component analysis (PCA). The first principal component (PC1) extracted from the δ18O TR records shows a positive/negative relationship with the annual Niño 3.4 index/southern oscillation index (SOI), with correlation coefficients higher than those between single δ18O TR record and the Niño 3.4 index/SOI, suggesting the ENSO signal is improved by PCA. A 31-year running correlation on PC1- Niño 3.4 index/SOI reveals an increasingly stronger correlation between δ18O TR and ENSO since the last century, inferring that, in the EAM region, the δ18O TR -ENSO correlation may become much stronger under continuous global warming in the future. Spectrum and spatial correlation analysis further support the idea that PC1 responds to ENSO. The significant relationships between observational precipitation δ18O and Niño 3.4 SST anomaly and PC1 from 1973–2003 CE suggest that precipitation δ18O is a key link to connect δ18O TR with ENSO. This study shows the advantage of ensemble data analysis on δ18O TR records in EAM region of China, which could better extract ENSO signals and reduce the uncertainties of reconstructed ENSO variations by individual δ18O TR records from the EAM region of China. It provides an alternative independent annual indicator for ENSO reconstruction on long time scales when more δ18O TR records from this region are extended in the near future. [ABSTRACT FROM AUTHOR]

The Asian summer monsoon (ASM) regulates water vapor and heat transport across the East Asian continent and has a significant impact on patterns of regional precipitation. However, assessment of the long-term association between the monsoon and precipitation in different regions remains difficult due to spatial chronological differences and uncertainties in interpretation of climate proxies. This study provides a novel insight into the interpretation of stalagmite oxygen isotopes (δ18O) records and obtained synchronous ASM index series and precipitation variations in Northern China (NC), Central China (CC), and Southwestern China (SWC) over the last 1134 years (850–1983CE). The results show that the ASM index sequence is consistent with the trend evident in the monsoon intensity records from the region upstream of the water vapor source, which represents the response to the inter-hemispheric temperature dominated by effective solar radiation (ESR). Reconstruction precipitation data were in general agreement with the existing paleo-hydrological records of the regions, confirming the reliability and chronological accuracy of the reconstruction. Correlation analysis highlighted the significant regional heterogeneity in the destabilizing relationship between precipitation and the monsoon over the past millennium in Eastern China at sub-centennial scales. Specifically, the precipitation-monsoon relationships in three regions, NC, CC, and SWC, might be related to the North Atlantic Oscillation (NAO), the position of the intertropical convergence zone (ITCZ), and solar activity, respectively. Moreover, at the millennial scale, a certain positive correlation between precipitation and ASM in NC and SWC was identified, whereas there was a weaker correlation between precipitation and ASM in CC. This study represents an attempt to further interpret the stalagmite δ18O record, which can be generalized to larger and longer time scales. • A novel method is proposed to reconstruct regional precipitation in East China by removing the monsoon effect from stalagmite δ18O. • High-resolution precipitation for North, Central and Southwest China during 850–1983CE were successfully reconstructed and supported by existing records. • The ASM-precipitation relationship may have been influenced by NAO, ITCZ and solar variability on sub-centennial scales. [ABSTRACT FROM AUTHOR]

Several recent studies have used records of the radiocarbon ( 14 C) bomb peak in speleothems to inversely model the soil a 14 CO 2 and the age distribution of soil organic material (SOM) above caves, in part to investigate the potential of speleothems as sensitive records of past SOM dynamics. The results of these modeling studies have suggested that soil CO 2 at karst sites is derived primarily from the decomposition of SOM with turnover times on the order of decades to centuries. This result is in stark contrast with observations of soil a 14 CO 2 at non-karst sites, which indicate that soil CO 2 is derived primarily from root respiration and decomposition of SOM with much shorter turnover times. This discrepancy suggests that SOM in karst settings may have a very different age distribution than sites that have been studied previously and/or that soil CO 2 is not the main source of speleothem carbon. To help resolve this discrepancy, we present an improved inverse model which we use to estimate the age of CO 2 above several caves. We also present results from a detailed case study of soil carbon dynamics at Heshang Cave, China. This work demonstrates that SOM in karst sites may be much older than SOM in non-karst soils that have been studied previously, but that CO 2 produced in the shallow soil zone is unlikely to be the main source of speleothem carbon. A review of the literature suggests that the most likely explanation for the aforementioned discrepancy is that decomposition of down-washed SOM in the vadose zone is the dominant source of speleothem carbon. [ABSTRACT FROM AUTHOR]

Northern Thailand is the most flood-prone region in Thailand during the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO) events. An annual growth rate profile covering the period from 1622 to 2008 AD was derived from the laminated stalagmite NJ-0901 from this area. By comparing stalagmite NJ-0901 to a contemporaneous stalagmite from the same cave and correlating the growth rate of NJ-0901 with meteorological data from the most recent 100 years, the stalagmite record proved to be a paleoclimate proxy of Thailand monsoon (TM) rainfall. This is the first annually laminated speleothem record that has been traced back four centuries. This record provided a long-term perspective and a valuable insight into TM rainfall and allowed us to investigate variations in the monsoon activity that was associated with IOD and ENSO. Our results indicate that both IOD and ENSO are significant climate modes that impact TM rainfall, but the effect of the interaction IOD and ENSO on TM rainfall remains unclear. [ABSTRACT FROM AUTHOR]

Abstract: In order to investigate how lipids in cave water respond to seasonal climate change, drip water samples were collected from 2006 to 2008 in Heshang Cave, central China for fatty acid analysis. These lipids are abundant in the drip water. Their compositions are dominated by lower-molecular-weight nC16:0, nC18:0 and nC14:0 acids, together with mono-unsaturated nC18:1, nC16:1 and nC14:1. Analysis of one water sample revealed marked differences between the dissolved and particulate fractions. The dissolved fraction contains total fatty acids one order of magnitude higher than that of the particulate fraction. The distributional patterns of the fatty acids suggest that microbes living in the overlying soils and/or groundwater system contribute most fatty acids to the drip water. This 2-a monitoring experiment reveals that the abundance of mono-unsaturated fatty acids relative to the saturated homologues (nC16:1/nC16:0 and nC18:1/nC18:0) relate inversely to the changes of synchronous external air temperature. Higher values occur under cold conditions (winter/spring), while lower values appear in warm intervals (summer). Further studies are needed to elucidate the dynamic processes by which the external temperature affects fatty acids in drip water and to confirm the potential application of fatty acid ratios such as nC16:1/nC16:0 and nC18:1/nC18:0 in paleotemperature reconstructions. [Copyright &y& Elsevier]