Stable isotopes in tree-ring cellulose provide important data in ecological,archaeological,and paleoenvironmental researches,thereby,the demand for stable isotope analyses is increasing rapidly.Simultaneous measuremen...Stable isotopes in tree-ring cellulose provide important data in ecological,archaeological,and paleoenvironmental researches,thereby,the demand for stable isotope analyses is increasing rapidly.Simultaneous measurement of cellulose δC and δO values from tree rings would reduce the cost of isotopic commodities and improve the analytical efficiency compared with conventional separate measurement.In this study,we compared the δC and δO values of tree-ringα-cellulose from Tianshan spruce(Picea schrenkiana)in an arid site in the drainage basin of the Urumqi River in Xinjiang of northwestern China based on separate and simultaneous measurements,using the combustion method(at1050°C)and the high-temperature pyrolysis method(at 1350°C and 1400°C).We verified the results of simultaneous measurement using the outputs from separate measurement and found that both methods(separate and simultaneous)produced similar δC values.The two-point calibrated method improved the results(range and variation)of δC and δO values.The mean values,standard deviations,and trends of the tree-ring δC obtained by the combustion method were similar to those by the pyrolysis method followed by two-point calibration.The simultaneously measured δO from the pyrolysis method at 1400°C had a nearly constant offset with that the pyrolysis method at 1350°C due to isotopic-dependence on the reaction temperature.However,they showed similar variations in the time series.The climate responses inferred from simultaneously and separately measured δC and δO did not differ between the two methods.The tree-ring δC and δO values were negatively correlated with standardized precipitation evapotranspiration index from May to August.In addition,the δO was significantly correlated with temperature(positive),precipitation(negative),and relative humidity(negative)from May to August.The tree-ring δC and δO values determined simultaneously through the high-temperature pyrolysis method could produce acceptable and reliable stable isotope series.The simultaneous isotopic measurement can greatly reduce the cost and time requirement compared with the separate isotopic measurement.These results are consistent with the previous studies at humid sites,suggesting that the simultaneous determination of δC and δO in tree-ringα-cellulose can be used in wide regions.展开更多
High-resolution tree-ring δ18O chronologies covering the last millennium,although scarce,are essential in understanding patterns of climatic changes in the northeastern region of the Qinghai-Tibetan Plateau.For this ...High-resolution tree-ring δ18O chronologies covering the last millennium,although scarce,are essential in understanding patterns of climatic changes in the northeastern region of the Qinghai-Tibetan Plateau.For this study,a tree-ring δ18O chronology with a temporal resolution of 3-years was developed from the long-lived Qilian juniper(Sabina przewalskii Kom.),extending back in time to AD 991.This long δ18O chronology was significantly correlated with the yearly δ18O in tree rings during the common period from 1800 to 2006,and was an effective proxy for relative humidity during the growing season.A low-frequency moisture pattern signified the occurrence of a slight drought during the Medieval Climate Anomaly,a marked occurrence of a wet period during the Little Ice Age,and a trend in increasing moisture levels,although lower than average,alongside the Twentieth Century warming trend.Comparisons to other hydroclimatic reconstructions indicate that this tree-ring18O chronology serves as a reliable paleo-humidity proxy for the Qaidam Basin as well as documenting details of past humidity levels in the region.展开更多
This review highlights work from the authors' laboratory on the recent development of seed-mediated growth method for noble metal nanocrystals. The seed-mediated growth method has become one of the most efficient ...This review highlights work from the authors' laboratory on the recent development of seed-mediated growth method for noble metal nanocrystals. The seed-mediated growth method has become one of the most efficient and versatile methods for synthe-sizing high-quality noble metal nanocrystals. The seed-mediated growth method can separate the nucleation and growth stages of metal nanocrystals, and thus provide better control over the size, size distribution, and crystallographic evolution of metal nanocrystals. Because of its high controllability, the seed-mediated growth method is especially promising in providing mechanistic insights into the growth mechanisms of noble metal nanocrystals. In this review, the thermodynamic and kinetic parameters for the nucleation and growth of noble metal nanocrystals are systematically summarized. Mechanistic understanding of these parameters is provided. These studies provide useful guidelines for the rational design and synthesis of novel noble metal nanocrystals with high quality.展开更多
基金funded by the National Natural Science Foundation of China (41501049, 41571196)the Self-determination Project of the State Key Laboratory of Cryospheric Sciences (SKLCS-ZZ-2018)+3 种基金the "Light of West China" Program of the Chinese Academy of Sciencesthe Youth Innovation Promotion Association, Chinese Academy of Sciences (2016372)the Chinese Scholarship Council (201704910171)the Fundamental Research Funds for the Central Universities (GK201801007)
文摘Stable isotopes in tree-ring cellulose provide important data in ecological,archaeological,and paleoenvironmental researches,thereby,the demand for stable isotope analyses is increasing rapidly.Simultaneous measurement of cellulose δC and δO values from tree rings would reduce the cost of isotopic commodities and improve the analytical efficiency compared with conventional separate measurement.In this study,we compared the δC and δO values of tree-ringα-cellulose from Tianshan spruce(Picea schrenkiana)in an arid site in the drainage basin of the Urumqi River in Xinjiang of northwestern China based on separate and simultaneous measurements,using the combustion method(at1050°C)and the high-temperature pyrolysis method(at 1350°C and 1400°C).We verified the results of simultaneous measurement using the outputs from separate measurement and found that both methods(separate and simultaneous)produced similar δC values.The two-point calibrated method improved the results(range and variation)of δC and δO values.The mean values,standard deviations,and trends of the tree-ring δC obtained by the combustion method were similar to those by the pyrolysis method followed by two-point calibration.The simultaneously measured δO from the pyrolysis method at 1400°C had a nearly constant offset with that the pyrolysis method at 1350°C due to isotopic-dependence on the reaction temperature.However,they showed similar variations in the time series.The climate responses inferred from simultaneously and separately measured δC and δO did not differ between the two methods.The tree-ring δC and δO values were negatively correlated with standardized precipitation evapotranspiration index from May to August.In addition,the δO was significantly correlated with temperature(positive),precipitation(negative),and relative humidity(negative)from May to August.The tree-ring δC and δO values determined simultaneously through the high-temperature pyrolysis method could produce acceptable and reliable stable isotope series.The simultaneous isotopic measurement can greatly reduce the cost and time requirement compared with the separate isotopic measurement.These results are consistent with the previous studies at humid sites,suggesting that the simultaneous determination of δC and δO in tree-ringα-cellulose can be used in wide regions.
基金supported by the Global Change Research Program of China (2010CB951401)the National Natural Science Foundation of China (41171167 and 40871002)
文摘High-resolution tree-ring δ18O chronologies covering the last millennium,although scarce,are essential in understanding patterns of climatic changes in the northeastern region of the Qinghai-Tibetan Plateau.For this study,a tree-ring δ18O chronology with a temporal resolution of 3-years was developed from the long-lived Qilian juniper(Sabina przewalskii Kom.),extending back in time to AD 991.This long δ18O chronology was significantly correlated with the yearly δ18O in tree rings during the common period from 1800 to 2006,and was an effective proxy for relative humidity during the growing season.A low-frequency moisture pattern signified the occurrence of a slight drought during the Medieval Climate Anomaly,a marked occurrence of a wet period during the Little Ice Age,and a trend in increasing moisture levels,although lower than average,alongside the Twentieth Century warming trend.Comparisons to other hydroclimatic reconstructions indicate that this tree-ring18O chronology serves as a reliable paleo-humidity proxy for the Qaidam Basin as well as documenting details of past humidity levels in the region.
基金supported by the National Natural Science Foundation of China (21175126)
文摘This review highlights work from the authors' laboratory on the recent development of seed-mediated growth method for noble metal nanocrystals. The seed-mediated growth method has become one of the most efficient and versatile methods for synthe-sizing high-quality noble metal nanocrystals. The seed-mediated growth method can separate the nucleation and growth stages of metal nanocrystals, and thus provide better control over the size, size distribution, and crystallographic evolution of metal nanocrystals. Because of its high controllability, the seed-mediated growth method is especially promising in providing mechanistic insights into the growth mechanisms of noble metal nanocrystals. In this review, the thermodynamic and kinetic parameters for the nucleation and growth of noble metal nanocrystals are systematically summarized. Mechanistic understanding of these parameters is provided. These studies provide useful guidelines for the rational design and synthesis of novel noble metal nanocrystals with high quality.
