The optimum multiparameter(OMP) method was often used to determine the percentages of water masses based on temperature, salinity and other parameters, like nutrient or dissolved oxygen(DO). There are a number of wate...The optimum multiparameter(OMP) method was often used to determine the percentages of water masses based on temperature, salinity and other parameters, like nutrient or dissolved oxygen(DO). There are a number of water masses in the East China Sea(ECS), a marginal sea of the western Pacific Ocean. However, it is difficult to clarify the proportion of water masses using traditional parameters, such as temperature, salinity, nutrient or DO because of the occurring of intensive biogeochemical processes in the near shore and shelf areas. Here, we reported the use of ^(234)U/^(238)Uactivity ratio embedded in the OMP method. The results indicate that seawater in the northern ECS mainly consisted of the estuarine water of Changjiang River(CEW), Kuroshio water(KW), and Yellow Sea Coastal Current(YSCC). In March 2017, the CEW only influenced the offshore waters shallower than30 m;the KW affected the east edge and the YSCC contributed more than 75% in the northern ECS.展开更多
The rare isotope ^236U has a half-life of 2.342（3）×107 years, and is produced principally by thermal neutron capture on ^235U. The isotopic atom ratio of ^236U/^238U depends on the integral thermal neutron flux...The rare isotope ^236U has a half-life of 2.342（3）×107 years, and is produced principally by thermal neutron capture on ^235U. The isotopic atom ratio of ^236U/^238U depends on the integral thermal neutron flux received by the material of interest. ^236U is potentially useful as a ＂fingerprint＂ for indicating the presence of neutron-irradiated uranium usually originating from nuclear activity. By extracting negative molecular ion UO^- from the uranium oxide target, simulating the ^236U^16O^- beam transport with ^238U^16O^- and ^208Pb2^16O^- pilot molecular ion beam, transporting the ^236U-containing ion beam with a high resolution injection magnet analyzer and electrostatic analyzer system, and finally identifying and detecting ^236U with a time-of-flight detector （TOF）, a method for AMS （Accelerator Mass Spectrometry） measurement of ^236U was established on the HI-13 Accelerator AMS system at China Institute of Atomic Energy.展开更多
The abundances of heavy elements produced in r-process nucleosynthesis in the early solar system need experimental verification.^(244)Pu could be the heaviest primordial nuclide produced before the formation of the Ea...The abundances of heavy elements produced in r-process nucleosynthesis in the early solar system need experimental verification.^(244)Pu could be the heaviest primordial nuclide produced before the formation of the Earth still being detectable today.As recent attempts failed to confirm the discovery of ^(244)Pu signals at a concentration of 1.0×10^(-18)g/g in bastnaesite reported by Hoffman et al.in this study,the total primordial ^(244)Pu in 450 g bastnaesite sample from Bayan Obo ore (China) was measured using ultrasensitive compact accelerator mass spectrometry (AMS).As no ^(244)Pu signal was detected,an upper limit for the ^(244)Pu in our bastnaesite sample was estimated to be 2.1×10^(-20)g/g at 99%confidence level.展开更多
Asian dust comprises a large portion of the northern hemisphere atmospheric dust load,thereby exerting substantial influence on the Earth’s climate,global biogeochemistry and hydrological cycle through accelerated sn...Asian dust comprises a large portion of the northern hemisphere atmospheric dust load,thereby exerting substantial influence on the Earth’s climate,global biogeochemistry and hydrological cycle through accelerated snow and ice melt.Dust deposited on alpine glaciers encodes information on broad scale atmospheric-environmental processes.The(^(234)U/^(238)U)values of dust fine particulates can reflect the comminuting time and intermediate processes;thus,it provides a new method for the provenance of aeolian dust in the glacial snowpack/cryoconite.Here we present results from a comprehensive survey of uranium isotopic concentrations in dust collected from cryoconites on the glaciers of the northern Tibetan Plateau(TP).These results indicate significant spatial heterogeneity in the(^(234)U/^(238)U)values associated with snowpack/cryoconite dust over a broad range of glaciers in the northern TP.The values of the(^(234)U/^(238)U)ratio in the glaciers of western Qilian Mountains(Qiyi Glacier,Shiyi Glacier,Laohugou Glacier No.12)were the highest,followed by the Tanggula(Dunkemadi Glacier)and Kunlun Mountains(Yuzhufeng Glacier),whereas these values were the lowest in the eastern Qilian Mountains(Jingyangling Snowpack,Dabanshan Snowpack,Lenglongling Glacier).By including the analysis of Sr-Nd isotopic compositions,we find the spatial isotopic distribution reflects a combination of local dust,which is associated with short comminuting times,and dust transported over long ranges.Meteorological data indicate that the dust production in the west and north TP,Alxa arid lands and Gobi Deserts,may have a significant impact on the TP glaciers.Moreover,U-Sr-Nd isotopic composition and end-member mixing models(EMMA)were used in our study to find out the relative contribution of distinct Asian dust sources to the dust budget in the TP glaciers.The results reveal that snowpack/cryoconite dust is derived from both local sources(low comminution signatures)as well as other dust sources in the Asian region.Our study demonstrates the potential of U isotope composition as a dust tracing method.In particular,by investigating this composition on dust collected from glacier snowpack and cryoconite holes,we arrive at a map of the distribution characteristics of(^(234)U/^(238)U)values in different regions of the TP.Our study is the first to deploy uranium comminution age for Tibetan dust source tracing,and the results are important to elucidate the multiple origins and dynamics of dust in the Tibetan Plateau.展开更多
基金The National Natural Science Foundation of China under contract Nos 41876077 and 41530965the National Key Research and Development Program of China under contract No.2016YFA0601300。
文摘The optimum multiparameter(OMP) method was often used to determine the percentages of water masses based on temperature, salinity and other parameters, like nutrient or dissolved oxygen(DO). There are a number of water masses in the East China Sea(ECS), a marginal sea of the western Pacific Ocean. However, it is difficult to clarify the proportion of water masses using traditional parameters, such as temperature, salinity, nutrient or DO because of the occurring of intensive biogeochemical processes in the near shore and shelf areas. Here, we reported the use of ^(234)U/^(238)Uactivity ratio embedded in the OMP method. The results indicate that seawater in the northern ECS mainly consisted of the estuarine water of Changjiang River(CEW), Kuroshio water(KW), and Yellow Sea Coastal Current(YSCC). In March 2017, the CEW only influenced the offshore waters shallower than30 m;the KW affected the east edge and the YSCC contributed more than 75% in the northern ECS.
基金Supported by NSAF (National Nature Science Fundation-China Academy of Engineering Physics Fundation) (10576040)
文摘The rare isotope ^236U has a half-life of 2.342（3）×107 years, and is produced principally by thermal neutron capture on ^235U. The isotopic atom ratio of ^236U/^238U depends on the integral thermal neutron flux received by the material of interest. ^236U is potentially useful as a ＂fingerprint＂ for indicating the presence of neutron-irradiated uranium usually originating from nuclear activity. By extracting negative molecular ion UO^- from the uranium oxide target, simulating the ^236U^16O^- beam transport with ^238U^16O^- and ^208Pb2^16O^- pilot molecular ion beam, transporting the ^236U-containing ion beam with a high resolution injection magnet analyzer and electrostatic analyzer system, and finally identifying and detecting ^236U with a time-of-flight detector （TOF）, a method for AMS （Accelerator Mass Spectrometry） measurement of ^236U was established on the HI-13 Accelerator AMS system at China Institute of Atomic Energy.
基金financially supported by the National Natural Science Foundation of China (Nos. 11675150, 12005197 and 12175201)。
文摘The abundances of heavy elements produced in r-process nucleosynthesis in the early solar system need experimental verification.^(244)Pu could be the heaviest primordial nuclide produced before the formation of the Earth still being detectable today.As recent attempts failed to confirm the discovery of ^(244)Pu signals at a concentration of 1.0×10^(-18)g/g in bastnaesite reported by Hoffman et al.in this study,the total primordial ^(244)Pu in 450 g bastnaesite sample from Bayan Obo ore (China) was measured using ultrasensitive compact accelerator mass spectrometry (AMS).As no ^(244)Pu signal was detected,an upper limit for the ^(244)Pu in our bastnaesite sample was estimated to be 2.1×10^(-20)g/g at 99%confidence level.
基金funded by the National Natural Science Foundation of China(Grant No.42022002)the State Key Laboratory of Cryosphere Sciences(Grant No.SKLCS-ZZ-2022)+1 种基金funded through NSF Critical Zone Collaborative proposal#2011910the German Research Foundation(DFG)for funding through the Heisenberg Programme“Multiscale Simulation of Earth Surface Processes”.
文摘Asian dust comprises a large portion of the northern hemisphere atmospheric dust load,thereby exerting substantial influence on the Earth’s climate,global biogeochemistry and hydrological cycle through accelerated snow and ice melt.Dust deposited on alpine glaciers encodes information on broad scale atmospheric-environmental processes.The(^(234)U/^(238)U)values of dust fine particulates can reflect the comminuting time and intermediate processes;thus,it provides a new method for the provenance of aeolian dust in the glacial snowpack/cryoconite.Here we present results from a comprehensive survey of uranium isotopic concentrations in dust collected from cryoconites on the glaciers of the northern Tibetan Plateau(TP).These results indicate significant spatial heterogeneity in the(^(234)U/^(238)U)values associated with snowpack/cryoconite dust over a broad range of glaciers in the northern TP.The values of the(^(234)U/^(238)U)ratio in the glaciers of western Qilian Mountains(Qiyi Glacier,Shiyi Glacier,Laohugou Glacier No.12)were the highest,followed by the Tanggula(Dunkemadi Glacier)and Kunlun Mountains(Yuzhufeng Glacier),whereas these values were the lowest in the eastern Qilian Mountains(Jingyangling Snowpack,Dabanshan Snowpack,Lenglongling Glacier).By including the analysis of Sr-Nd isotopic compositions,we find the spatial isotopic distribution reflects a combination of local dust,which is associated with short comminuting times,and dust transported over long ranges.Meteorological data indicate that the dust production in the west and north TP,Alxa arid lands and Gobi Deserts,may have a significant impact on the TP glaciers.Moreover,U-Sr-Nd isotopic composition and end-member mixing models(EMMA)were used in our study to find out the relative contribution of distinct Asian dust sources to the dust budget in the TP glaciers.The results reveal that snowpack/cryoconite dust is derived from both local sources(low comminution signatures)as well as other dust sources in the Asian region.Our study demonstrates the potential of U isotope composition as a dust tracing method.In particular,by investigating this composition on dust collected from glacier snowpack and cryoconite holes,we arrive at a map of the distribution characteristics of(^(234)U/^(238)U)values in different regions of the TP.Our study is the first to deploy uranium comminution age for Tibetan dust source tracing,and the results are important to elucidate the multiple origins and dynamics of dust in the Tibetan Plateau.
