The chronology of geological records in lacustrine, peatland and marine sediments for the late glacial depends mainly on 14C dating technology, which provides the basic database for global paleoclimate research. However, 14C reservoir correction always challenges the accuracy of the 14C chronology of terrestrial and marine sediments and the uncertainty of the 14C chronology associated with the carbon reservoir effect becomes critical for high resolution paleoclimate studies. Here, based on the hypothesis of synchronization of precipitation isotopes, we verify and identify a series of in-phase points of precipitation isotopes (IPPIs) between sediment leaf-wax hydrogen and stalagmite-calcite oxygen isotopes. Because stalagmite oxygen isotope records are accurately dated by U–Th dating technology, the ages of stalagmite IPPIs could be used to improve 14C reservoir correction of lacustrine IPPIs. We found that reservoir-corrected 14C ages of lacustrine, peat, and marine IPPIs are scattered with an average uncertainty of 1 ka when compared with the corresponding IPPIs on U–Th age scales. We suggest that the reservoir age correction at different time intervals could be further adjusted by using the U–Th age-backed IPPIs, which largely reduces the uncertainty of the 14C chronology and thus provides more accurate paleoclimate records.
A: Below-cloud evaporation calculated by isotope Stewart (1975) suggested the falling raindrop isotopic fractionation of evaporation could be calculated according to the fraction of raindrop mass remained after evaporation:
In this article, the equilibrium behavior of solutions of 1-ethyl-3-methylimidazolium dimethyl phosphate ([Emim]DMP) and ethyl acetate or acetone in aqueous two-phase system (ATPS) was discussed to understand the liquid–liquid equilibrium (LLE) behavior of these organic solvents. Thus, we determined phase diagrams and LLE data at 303.15, 308.15, 313.15, and 323.15 K for the investigated biphasic systems. Four empirical equations were used to study the tie lines. The results showed that for the [Emim]DMP + acetone + water biphasic systems within the investigated temperature range, temperature influences the phase behavior, but for the [Emim]DMP + ethyl acetate + water biphasic systems within the investigated temperature range, there are no notable changes on the phase behavior with rising temperature. The results may have important applications for the separation of antibiotics and for the recovery of ionic liquids (ILs).
Abstract. Below-cloud evaporation effect heavily alters the initial precipitation isotopic composition, especially in the arid and semi-arid regions, and leads to misinterpreting the isotopic signal. To correctly explore the information contained in the precipitation isotopes, the first step is to qualitatively analyze the falling raindrops encountered below-cloud processes, and then to quantitatively compute the below-cloud evaporation ratio of raindrops. Here, based on two-year precipitation and water vapor isotopic observations in Xi'an, we systematically evaluated the variations of precipitation and water vapor isotopes caused by the below-cloud evaporation effect. Our results suggest that the equilibrium method could be successfully used to predict the ground-level water vapor isotopic composition in semi-arid climates, especially for the winter data. Moreover, by using △d△δ-diagram, our data showed that evaporation is the mainly happened below-cloud process of raindrops, while snowfall samples retained the initial cloud signal because of less isotopic exchange between vapor and solid phases. In terms of meteorological factors, both temperature, relative humidity, and precipitation amount affect the intensity of below-cloud evaporation. In arid and semi-arid regions, the below-cloud evaporation ratio computed by the mass conservation equation would be overestimated relative to the isotopic method, while relative humidity is the most sensitive parameter in computing the remaining fraction of evaporation. In the Chinese Loess Plateau (CLP) city, raindrops are weakly evaporated in autumn and winter, and heavily evaporated in spring and summer, and in the meantime, the evaporation intensity is related to the local relative humidity. Our work sets an integrated and effective method to evaluate the below-cloud evaporation effect, and it will improve our understanding of the information contained in precipitation isotopic signals.
Land snails are abundant and well preserved in loess-paleosol sequences on the Chinese Loess Plateau (CLP) and are often regarded as valuable climatic indicators in paleoclimate reconstruction. To date, many stable isotope investigations have been carried out on land snail shells (e.g., δ13Cshell and δ18Oshell) from diverse geographical and climatic regions. However, few studies have been conducted on modern minute land snails (2–10 mm) on the CLP, and their climatic significance has not been adequately understood. Here, we present new δ13Cshell and δ18Oshell data from four minute modern land snails (Pupilla aeoli, Gastrocopta armigerella, Opeas striatissimum, Vallonia tenera), and analyses of their correlations with climatic factors (growing season temperature, precipitation and relative humidity) were conducted to examine their climatic significance across the CLP. The results show that δ13Cshell can record local vegetation information and has the potential to be a reliable precipitation proxy. Interestingly, δ18Oshell exhibits spatially scattered values in the studied region, and these data yielded poor correlations with various climatic parameters, such as precipitation amount, temperature and relative humidity. Given the similar spatial characteristics of observed precipitation δ18O (δ18Op), these phenomena may support the dominant control of δ18Op on δ18Oshell.
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